diff --git a/CHANGELOG.md b/CHANGELOG.md
index ec35d041d..cbad9612e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,7 +10,7 @@ _None_
 
 ### New Features
 
-_None_
+- `upload_github_release_assets` action: uploads assets on an existing GitHub release without disturbing unrelated assets. If assets exists already, it replaces them. [#743]
 
 ### Bug Fixes
 
diff --git a/lib/fastlane/plugin/wpmreleasetoolkit/actions/common/upload_github_release_assets_action.rb b/lib/fastlane/plugin/wpmreleasetoolkit/actions/common/upload_github_release_assets_action.rb
new file mode 100644
index 000000000..7e951c316
--- /dev/null
+++ b/lib/fastlane/plugin/wpmreleasetoolkit/actions/common/upload_github_release_assets_action.rb
@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+
+require 'fastlane/action'
+require_relative '../../helper/github_helper'
+
+module Fastlane
+  module Actions
+    class UploadGithubReleaseAssetsAction < Action
+      def self.run(params)
+        repository = params[:repository]
+        version = params[:version]
+        assets = params[:release_assets]
+        replace_existing = params[:replace_existing]
+
+        UI.message("Uploading #{assets.count} GitHub Release asset(s) to #{repository} #{version}.")
+
+        github_helper = Fastlane::Helper::GithubHelper.new(github_token: params[:github_token])
+        url = github_helper.upload_release_assets(
+          repository: repository,
+          version: version,
+          assets: assets,
+          replace_existing: replace_existing
+        )
+
+        UI.success("Successfully uploaded GitHub Release assets. You can see the release at '#{url}'")
+        url
+      end
+
+      def self.description
+        'Uploads assets to an existing GitHub Release'
+      end
+
+      def self.authors
+        ['Automattic']
+      end
+
+      def self.return_value
+        'The URL of the GitHub Release'
+      end
+
+      def self.details
+        'Uploads assets to an existing GitHub Release. By default, existing release assets with matching filenames are replaced; when replace_existing is false, matching assets cause the action to fail.'
+      end
+
+      def self.available_options
+        [
+          FastlaneCore::ConfigItem.new(key: :repository,
+                                       description: 'The slug (`<org>/<repo>`) of the GitHub repository containing the release',
+                                       optional: false,
+                                       type: String,
+                                       verify_block: proc do |value|
+                                         UI.user_error!('Repository cannot be empty') if value.to_s.empty?
+                                       end),
+          FastlaneCore::ConfigItem.new(key: :version,
+                                       description: 'The version of the release. Used as the git tag name',
+                                       optional: false,
+                                       type: String,
+                                       verify_block: proc do |value|
+                                         UI.user_error!('Version cannot be empty') if value.to_s.empty?
+                                       end),
+          FastlaneCore::ConfigItem.new(key: :release_assets,
+                                       description: 'Assets to upload',
+                                       type: Array,
+                                       optional: false,
+                                       verify_block: proc do |value|
+                                         UI.user_error!('You must provide at least one release asset') if value.nil? || value.empty?
+                                         value.each do |asset|
+                                           UI.user_error!('release_assets must contain file paths') unless asset.is_a?(String) && !asset.empty?
+                                         end
+                                       end),
+          FastlaneCore::ConfigItem.new(key: :replace_existing,
+                                       description: 'True to delete existing release assets with matching filenames before uploading. False to fail if a matching asset exists',
+                                       optional: true,
+                                       default_value: true,
+                                       type: Boolean),
+          Fastlane::Helper::GithubHelper.github_token_config_item,
+        ]
+      end
+
+      def self.is_supported?(platform)
+        true
+      end
+    end
+  end
+end
diff --git a/lib/fastlane/plugin/wpmreleasetoolkit/helper/github_helper.rb b/lib/fastlane/plugin/wpmreleasetoolkit/helper/github_helper.rb
index b8a89d27f..4da911573 100644
--- a/lib/fastlane/plugin/wpmreleasetoolkit/helper/github_helper.rb
+++ b/lib/fastlane/plugin/wpmreleasetoolkit/helper/github_helper.rb
@@ -192,6 +192,57 @@ def create_release(repository:, version:, description:, assets:, prerelease:, is
         release[:html_url]
       end
 
+      # Returns the GitHub release matching a given tag/version.
+      #
+      # @param [String] repository The repository to fetch the GitHub release from. Typically a repo slug (<org>/<repo>).
+      # @param [String] version The release version/tag to fetch.
+      # @return [Sawyer::Resource] The matching GitHub Release.
+      # @raise [Fastlane::UI::Error] UI.user_error! if the release does not exist.
+      #
+      def get_release(repository:, version:)
+        client.release_for_tag(repository, version)
+      rescue Octokit::NotFound
+        UI.user_error!("Could not find GitHub Release for tag #{version} in #{repository}")
+      end
+
+      # Uploads assets to an existing GitHub release, optionally replacing matching filenames.
+      #
+      # @param [String] repository The repository to upload the GitHub release assets to. Typically a repo slug (<org>/<repo>).
+      # @param [String] version The release version/tag to upload assets to.
+      # @param [Array<String>] assets List of local file paths to attach as release assets.
+      # @param [TrueClass|FalseClass] replace_existing Delete existing same-filename assets before uploading. When false, fail if a matching asset exists.
+      # @return [String] URL of the corresponding GitHub Release.
+      # @raise [Fastlane::UI::Error] UI.user_error! if the release or any local asset file does not exist.
+      #
+      def upload_release_assets(repository:, version:, assets:, replace_existing: true)
+        asset_paths = validate_release_assets!(assets)
+        release = get_release(repository: repository, version: version)
+        existing_assets = client.release_assets(release.url)
+
+        asset_paths.each do |file_path|
+          file_name = File.basename(file_path)
+          matching_assets = existing_assets.select { |asset| asset.name == file_name }
+
+          unless matching_assets.empty?
+            if replace_existing
+              matching_assets.each do |asset|
+                UI.message("Deleting existing GitHub Release asset #{asset.name}")
+                client.delete_release_asset(asset.url)
+              end
+              existing_assets -= matching_assets
+            else
+              UI.user_error!("GitHub Release #{version} already has an asset named #{file_name}. Set replace_existing: true to replace it.")
+            end
+          end
+
+          UI.message("Uploading #{file_path} to GitHub Release #{version}")
+          uploaded_asset = client.upload_asset(release.url, file_path, content_type: 'application/octet-stream')
+          existing_assets << uploaded_asset unless uploaded_asset.nil?
+        end
+
+        release.html_url
+      end
+
       # Use the GitHub API to generate release notes based on the list of PRs between current tag and previous tag.
       # @note This API uses the `.github/release.yml` config file to classify the PRs by category in the generated list according to PR labels.
       #
@@ -368,6 +419,26 @@ def set_branch_protection(repository:, branch:, **options)
         client.protect_branch(repository, branch, options)
       end
 
+      def validate_release_assets!(assets)
+        asset_paths = Array(assets)
+        UI.user_error!('You must provide at least one release asset') if asset_paths.empty?
+
+        asset_paths.each do |file_path|
+          UI.user_error!('release_assets must contain file paths') unless file_path.is_a?(String) && !file_path.empty?
+        end
+
+        file_names = asset_paths.map { |file_path| File.basename(file_path) }
+        UI.user_error!('release_assets must not contain duplicate filenames') if file_names.uniq.length != file_names.length
+
+        asset_paths.each do |file_path|
+          UI.user_error!("Can't find file #{file_path}!") unless File.file?(file_path)
+        end
+
+        asset_paths
+      end
+
+      private :validate_release_assets!
+
       # Convert a response from the `/branch-protection` API endpoint into a Hash
       # suitable to be returned and/or reused to pass to a subsequent `/branch-protection` API request
       # @param [Sawyer::Resource] response The API response returned by `#get_branch_protection` or `#set_branch_protection`
diff --git a/spec/github_helper_spec.rb b/spec/github_helper_spec.rb
index f30bacc48..fdb57a349 100644
--- a/spec/github_helper_spec.rb
+++ b/spec/github_helper_spec.rb
@@ -619,6 +619,174 @@ def create_release(is_draft:, assets: [], name: nil)
     end
   end
 
+  describe '#upload_release_assets' do
+    let(:test_repo) { 'repo-test/project-test' }
+    let(:test_version) { '1.0.0' }
+    let(:release_url) { 'https://api.github.com/repos/repo-test/project-test/releases/123' }
+    let(:release_html_url) { 'https://github.com/repo-test/project-test/releases/tag/1.0.0' }
+    let(:release) { sawyer_resource_stub(url: release_url, html_url: release_html_url) }
+    let(:existing_assets) { [] }
+    let(:uploaded_asset) { release_asset(name: 'test-app.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/999') }
+    let(:client) do
+      instance_double(
+        Octokit::Client,
+        user: instance_double('User', name: 'test'),
+        'auto_paginate=': nil
+      )
+    end
+    let(:helper) do
+      described_class.new(github_token: 'Fake-GitHubToken-123')
+    end
+
+    before do
+      allow(Octokit::Client).to receive(:new).and_return(client)
+      allow(client).to receive(:release_for_tag).with(test_repo, test_version).and_return(release)
+      allow(client).to receive(:release_assets).with(release_url).and_return(existing_assets)
+      allow(client).to receive_messages(upload_asset: uploaded_asset, delete_release_asset: true)
+    end
+
+    it 'fails clearly if the release does not exist' do
+      allow(client).to receive(:release_for_tag).with(test_repo, test_version).and_raise(Octokit::NotFound)
+
+      with_tmp_file(named: 'test-app.zip') do |file_path|
+        expect do
+          upload_release_assets(assets: [file_path])
+        end.to raise_error(FastlaneCore::Interface::FastlaneError, "Could not find GitHub Release for tag #{test_version} in #{test_repo}")
+      end
+    end
+
+    it 'fails clearly if an asset file does not exist' do
+      expect(client).not_to receive(:release_for_tag)
+      expect(client).not_to receive(:release_assets)
+      expect(client).not_to receive(:upload_asset)
+
+      expect do
+        upload_release_assets(assets: ['missing-file.zip'])
+      end.to raise_error(FastlaneCore::Interface::FastlaneError, "Can't find file missing-file.zip!")
+    end
+
+    it 'fails clearly if an asset is not a file path' do
+      expect(client).not_to receive(:release_for_tag)
+      expect(client).not_to receive(:release_assets)
+      expect(client).not_to receive(:upload_asset)
+
+      expect do
+        upload_release_assets(assets: [123])
+      end.to raise_error(FastlaneCore::Interface::FastlaneError, 'release_assets must contain file paths')
+    end
+
+    it 'fails without mutating GitHub when local assets have duplicate filenames' do
+      in_tmp_dir do |tmpdir|
+        first_dir = File.join(tmpdir, 'ios')
+        second_dir = File.join(tmpdir, 'tvos')
+        Dir.mkdir(first_dir)
+        Dir.mkdir(second_dir)
+
+        first_file_path = File.join(first_dir, 'test-app.zip')
+        second_file_path = File.join(second_dir, 'test-app.zip')
+        File.write(first_file_path, 'ios')
+        File.write(second_file_path, 'tvos')
+
+        expect(client).not_to receive(:release_for_tag)
+        expect(client).not_to receive(:release_assets)
+        expect(client).not_to receive(:delete_release_asset)
+        expect(client).not_to receive(:upload_asset)
+
+        expect do
+          upload_release_assets(assets: [first_file_path, second_file_path], replace_existing: false)
+        end.to raise_error(FastlaneCore::Interface::FastlaneError, 'release_assets must not contain duplicate filenames')
+      end
+    end
+
+    it 'uploads one asset to the existing release' do
+      with_tmp_file(named: 'test-app.zip') do |file_path|
+        expect(client).to receive(:upload_asset).with(release_url, file_path, { content_type: 'application/octet-stream' })
+
+        result = upload_release_assets(assets: [file_path])
+
+        expect(result).to eq(release_html_url)
+      end
+    end
+
+    it 'uploads multiple assets to the existing release' do
+      in_tmp_dir do |tmpdir|
+        first_file_path = File.join(tmpdir, 'test-ios.zip')
+        second_file_path = File.join(tmpdir, 'test-tvos.zip')
+        File.write(first_file_path, 'ios')
+        File.write(second_file_path, 'tvos')
+
+        first_uploaded_asset = release_asset(name: 'test-ios.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/1000')
+        second_uploaded_asset = release_asset(name: 'test-tvos.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/1001')
+
+        expect(client).to receive(:upload_asset).with(release_url, first_file_path, { content_type: 'application/octet-stream' }).ordered.and_return(first_uploaded_asset)
+        expect(client).to receive(:upload_asset).with(release_url, second_file_path, { content_type: 'application/octet-stream' }).ordered.and_return(second_uploaded_asset)
+
+        result = upload_release_assets(assets: [first_file_path, second_file_path])
+
+        expect(result).to eq(release_html_url)
+      end
+    end
+
+    it 'replaces an existing asset with the same filename' do
+      existing_asset = release_asset(name: 'test-app.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/1234')
+      allow(client).to receive(:release_assets).with(release_url).and_return([existing_asset])
+
+      with_tmp_file(named: 'test-app.zip') do |file_path|
+        expect(client).to receive(:delete_release_asset).with(existing_asset.url)
+        expect(client).to receive(:upload_asset).with(release_url, file_path, { content_type: 'application/octet-stream' })
+
+        result = upload_release_assets(assets: [file_path])
+
+        expect(result).to eq(release_html_url)
+      end
+    end
+
+    it 'preserves unrelated existing assets' do
+      matching_asset = release_asset(name: 'test-app.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/1234')
+      unrelated_asset = release_asset(name: 'other-platform.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/5678')
+      deleted_asset_urls = []
+
+      allow(client).to receive(:release_assets).with(release_url).and_return([matching_asset, unrelated_asset])
+      allow(client).to receive(:delete_release_asset) do |asset_url|
+        deleted_asset_urls << asset_url
+        true
+      end
+
+      with_tmp_file(named: 'test-app.zip') do |file_path|
+        upload_release_assets(assets: [file_path])
+      end
+
+      expect(deleted_asset_urls).to eq([matching_asset.url])
+    end
+
+    it 'fails without deleting or uploading when replace_existing is false and a matching asset exists' do
+      existing_asset = release_asset(name: 'test-app.zip', url: 'https://api.github.com/repos/repo-test/project-test/releases/assets/1234')
+      allow(client).to receive(:release_assets).with(release_url).and_return([existing_asset])
+
+      expect(client).not_to receive(:delete_release_asset)
+      expect(client).not_to receive(:upload_asset)
+
+      with_tmp_file(named: 'test-app.zip') do |file_path|
+        expect do
+          upload_release_assets(assets: [file_path], replace_existing: false)
+        end.to raise_error(FastlaneCore::Interface::FastlaneError, "GitHub Release #{test_version} already has an asset named test-app.zip. Set replace_existing: true to replace it.")
+      end
+    end
+
+    def upload_release_assets(assets:, replace_existing: true)
+      helper.upload_release_assets(
+        repository: test_repo,
+        version: test_version,
+        assets: assets,
+        replace_existing: replace_existing
+      )
+    end
+
+    def release_asset(name:, url:)
+      sawyer_resource_stub(name: name, url: url)
+    end
+  end
+
   describe '#github_token_config_item' do
     it 'has the correct key' do
       expect(described_class.github_token_config_item.key).to eq(:github_token)
diff --git a/spec/upload_github_release_assets_spec.rb b/spec/upload_github_release_assets_spec.rb
new file mode 100644
index 000000000..d53e5f8be
--- /dev/null
+++ b/spec/upload_github_release_assets_spec.rb
@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Fastlane::Actions::UploadGithubReleaseAssetsAction do
+  let(:test_token) { 'ghp_fake_token' }
+  let(:test_repo) { 'repo-test/project-test' }
+  let(:test_version) { '1.0.0' }
+  let(:test_assets) { ['builds/test-app.zip'] }
+  let(:test_url) { 'https://github.com/repo-test/project-test/releases/tag/1.0.0' }
+  let(:github_helper) { instance_double(Fastlane::Helper::GithubHelper) }
+
+  before do
+    allow(Fastlane::Helper::GithubHelper).to receive(:new).with(github_token: test_token).and_return(github_helper)
+  end
+
+  it 'uploads release assets and returns the release URL' do
+    allow(github_helper).to receive(:upload_release_assets).and_return(test_url)
+    expect(github_helper).to receive(:upload_release_assets).with(
+      repository: test_repo,
+      version: test_version,
+      assets: test_assets,
+      replace_existing: true
+    )
+
+    result = run_described_fastlane_action(
+      github_token: test_token,
+      repository: test_repo,
+      version: test_version,
+      release_assets: test_assets
+    )
+
+    expect(result).to eq(test_url)
+  end
+
+  it 'forwards replace_existing when provided' do
+    allow(github_helper).to receive(:upload_release_assets).and_return(test_url)
+    expect(github_helper).to receive(:upload_release_assets).with(
+      repository: test_repo,
+      version: test_version,
+      assets: test_assets,
+      replace_existing: false
+    )
+
+    result = run_described_fastlane_action(
+      github_token: test_token,
+      repository: test_repo,
+      version: test_version,
+      release_assets: test_assets,
+      replace_existing: false
+    )
+
+    expect(result).to eq(test_url)
+  end
+
+  it 'fails when release_assets is empty' do
+    expect do
+      run_described_fastlane_action(
+        github_token: test_token,
+        repository: test_repo,
+        version: test_version,
+        release_assets: []
+      )
+    end.to raise_error(FastlaneCore::Interface::FastlaneError, 'You must provide at least one release asset')
+  end
+
+  it 'fails when release_assets contains a non-path value' do
+    expect do
+      run_described_fastlane_action(
+        github_token: test_token,
+        repository: test_repo,
+        version: test_version,
+        release_assets: [123]
+      )
+    end.to raise_error(FastlaneCore::Interface::FastlaneError, 'release_assets must contain file paths')
+  end
+end