diff --git a/README.md b/README.md
index 72d9fdf73..533970b24 100644
--- a/README.md
+++ b/README.md
@@ -4696,6 +4696,62 @@ or return code 1 if it does not.
 
 
 
+### wp post convert-to-blocks
+
+Converts the classic (non-block) content of one or more posts to block markup.
+
+~~~
+wp post convert-to-blocks <id>... [--dry-run]
+~~~
+
+Uses the server-side block conversion provided by the Gutenberg plugin
+(see https://github.com/WordPress/gutenberg/pull/82013) to turn classic
+HTML content into serialized block markup. Markup that no block claims
+is kept verbatim inside a Custom HTML block, so nothing is lost. Posts
+that already contain blocks or have no content are skipped.
+
+The conversion does not sanitize the markup. Saving the converted content
+applies the usual kses filtering for the current user context, so a run
+without `--user` is filtered as an untrusted author would be. Run the
+command with `--user=<administrator>` to keep markup that requires the
+`unfiltered_html` capability, such as iframes or scripts.
+
+Requires a Gutenberg build that provides `gutenberg_html_to_block_markup()`.
+
+**OPTIONS**
+
+	<id>...
+		One or more IDs of posts to convert.
+
+	[--dry-run]
+		Preview which posts would be converted, without saving any changes.
+
+**EXAMPLES**
+
+    # Convert a single post.
+    $ wp post convert-to-blocks 123
+    Converted post 123.
+    Success: Converted 1 of 1 posts.
+
+    # Convert every post of a post type.
+    $ wp post list --post_type=post --format=ids | xargs wp post convert-to-blocks
+    Converted post 123.
+    Converted post 124.
+    Warning: Post 125 already contains blocks.
+    Success: Converted 2 of 3 posts (1 skipped).
+
+    # Preview a conversion without saving.
+    $ wp post convert-to-blocks 123 --dry-run
+    Would convert post 123.
+    Success: Would convert 1 of 1 posts.
+
+    # Run as an administrator to keep markup that requires unfiltered_html.
+    $ wp post convert-to-blocks 123 --user=admin
+    Converted post 123.
+    Success: Converted 1 of 1 posts.
+
+
+
 ### wp post block
 
 Manages blocks within post content.
diff --git a/composer.json b/composer.json
index fcd353184..2a3265ca2 100644
--- a/composer.json
+++ b/composer.json
@@ -148,6 +148,7 @@
             "post url-to-id",
             "post has-blocks",
             "post has-block",
+            "post convert-to-blocks",
             "post block",
             "post block clone",
             "post block count",
diff --git a/features/post-convert-to-blocks.feature b/features/post-convert-to-blocks.feature
new file mode 100644
index 000000000..7b1bff0d9
--- /dev/null
+++ b/features/post-convert-to-blocks.feature
@@ -0,0 +1,132 @@
+Feature: Convert classic post content to blocks
+
+  # The conversion depends on the server-side block conversion from
+  # https://github.com/WordPress/gutenberg/pull/82013 (branch
+  # `try/13163-php-block-conversion`), which no released Gutenberg build
+  # provides yet. The scenarios tagged @broken below need a Gutenberg build
+  # of that PR. To run them locally, build the plugin ZIP from that branch,
+  # remove the @broken tags, and add the following step after the
+  # `Given a WP install` step in each scenario:
+  #
+  #   And I run `wp plugin install /path/to/gutenberg.zip --activate`
+
+  Scenario: Conversion requires the Gutenberg build with server-side block conversion
+    Given a WP install
+
+    When I try `wp post convert-to-blocks 1`
+    Then STDERR should be:
+      """
+      Error: Server-side block conversion is not available. Activate the Gutenberg plugin from https://github.com/WordPress/gutenberg/pull/82013.
+      """
+    And STDOUT should be empty
+    And the return code should be 1
+
+  @broken
+  Scenario: Convert a classic post to blocks
+    Given a WP install
+
+    When I run `wp post create --post_title='Classic post' --post_content='<h2>Title</h2><p>Text</p>' --porcelain`
+    Then save STDOUT as {POST_ID}
+
+    When I run `wp post convert-to-blocks {POST_ID}`
+    Then STDOUT should be:
+      """
+      Converted post {POST_ID}.
+      Success: Converted 1 of 1 posts.
+      """
+    And STDERR should be empty
+
+    When I run `wp post get {POST_ID} --field=post_content`
+    Then STDOUT should contain:
+      """
+      <!-- wp:heading -->
+      """
+    And STDOUT should contain:
+      """
+      <!-- wp:paragraph -->
+      """
+
+    When I run `wp post has-blocks {POST_ID}`
+    Then STDOUT should be:
+      """
+      Success: Post {POST_ID} contains blocks.
+      """
+
+  @broken
+  Scenario: Preview a conversion with --dry-run
+    Given a WP install
+
+    When I run `wp post create --post_title='Classic post' --post_content='<h2>Title</h2><p>Text</p>' --porcelain`
+    Then save STDOUT as {POST_ID}
+
+    When I run `wp post convert-to-blocks {POST_ID} --dry-run`
+    Then STDOUT should be:
+      """
+      Would convert post {POST_ID}.
+      Success: Would convert 1 of 1 posts.
+      """
+    And STDERR should be empty
+
+    When I run `wp post get {POST_ID} --field=post_content`
+    Then STDOUT should be:
+      """
+      <h2>Title</h2><p>Text</p>
+      """
+
+  @broken
+  Scenario: Skip posts that already contain blocks
+    Given a WP install
+
+    When I run `wp post create --post_title='Block post' --post_content='<!-- wp:paragraph --><p>Text</p><!-- /wp:paragraph -->' --porcelain`
+    Then save STDOUT as {POST_ID}
+
+    When I try `wp post convert-to-blocks {POST_ID}`
+    Then STDERR should be:
+      """
+      Warning: Post {POST_ID} already contains blocks.
+      """
+    And STDOUT should be:
+      """
+      Success: Converted 0 of 1 posts (1 skipped).
+      """
+    And the return code should be 0
+
+  @broken
+  Scenario: Skip posts without content
+    Given a WP install
+
+    When I run `wp post create --post_title='Empty post' --post_content='' --porcelain`
+    Then save STDOUT as {POST_ID}
+
+    When I try `wp post convert-to-blocks {POST_ID}`
+    Then STDERR should be:
+      """
+      Warning: Post {POST_ID} has no content to convert.
+      """
+    And STDOUT should be:
+      """
+      Success: Converted 0 of 1 posts (1 skipped).
+      """
+    And the return code should be 0
+
+  @broken
+  Scenario: Report missing posts as failures
+    Given a WP install
+
+    When I run `wp post create --post_title='Classic post' --post_content='<p>Text</p>' --porcelain`
+    Then save STDOUT as {POST_ID}
+
+    When I try `wp post convert-to-blocks {POST_ID} 99999`
+    Then STDERR should contain:
+      """
+      Warning: Could not find the post with ID 99999.
+      """
+    And STDERR should contain:
+      """
+      Error: Only converted 1 of 2 posts (1 failed).
+      """
+    And STDOUT should be:
+      """
+      Converted post {POST_ID}.
+      """
+    And the return code should be 1
diff --git a/src/Post_Command.php b/src/Post_Command.php
index 41f3e1216..202bdab7d 100644
--- a/src/Post_Command.php
+++ b/src/Post_Command.php
@@ -1443,6 +1443,134 @@ public function has_block( $args, $assoc_args ) {
 		}
 	}
 
+	/**
+	 * Converts the classic (non-block) content of one or more posts to block markup.
+	 *
+	 * Uses the server-side block conversion provided by the Gutenberg plugin
+	 * (see https://github.com/WordPress/gutenberg/pull/82013) to turn classic
+	 * HTML content into serialized block markup. Markup that no block claims
+	 * is kept verbatim inside a Custom HTML block, so nothing is lost. Posts
+	 * that already contain blocks or have no content are skipped.
+	 *
+	 * The conversion does not sanitize the markup. Saving the converted content
+	 * applies the usual kses filtering for the current user context, so a run
+	 * without `--user` is filtered as an untrusted author would be. Run the
+	 * command with `--user=<administrator>` to keep markup that requires the
+	 * `unfiltered_html` capability, such as iframes or scripts.
+	 *
+	 * Requires a Gutenberg build that provides `gutenberg_html_to_block_markup()`.
+	 *
+	 * ## OPTIONS
+	 *
+	 * <id>...
+	 * : One or more IDs of posts to convert.
+	 *
+	 * [--dry-run]
+	 * : Preview which posts would be converted, without saving any changes.
+	 *
+	 * ## EXAMPLES
+	 *
+	 *     # Convert a single post.
+	 *     $ wp post convert-to-blocks 123
+	 *     Converted post 123.
+	 *     Success: Converted 1 of 1 posts.
+	 *
+	 *     # Convert every post of a post type.
+	 *     $ wp post list --post_type=post --format=ids | xargs wp post convert-to-blocks
+	 *     Converted post 123.
+	 *     Converted post 124.
+	 *     Warning: Post 125 already contains blocks.
+	 *     Success: Converted 2 of 3 posts (1 skipped).
+	 *
+	 *     # Preview a conversion without saving.
+	 *     $ wp post convert-to-blocks 123 --dry-run
+	 *     Would convert post 123.
+	 *     Success: Would convert 1 of 1 posts.
+	 *
+	 *     # Run as an administrator to keep markup that requires unfiltered_html.
+	 *     $ wp post convert-to-blocks 123 --user=admin
+	 *     Converted post 123.
+	 *     Success: Converted 1 of 1 posts.
+	 *
+	 * @subcommand convert-to-blocks
+	 */
+	public function convert_to_blocks( $args, $assoc_args ) {
+		if ( ! function_exists( 'gutenberg_html_to_block_markup' ) ) {
+			WP_CLI::error( 'Server-side block conversion is not available. Activate the Gutenberg plugin from https://github.com/WordPress/gutenberg/pull/82013.' );
+		}
+
+		$dry_run = (bool) Utils\get_flag_value( $assoc_args, 'dry-run', false );
+
+		$total     = count( $args );
+		$successes = 0;
+		$errors    = 0;
+		$skips     = 0;
+
+		foreach ( $args as $post_id ) {
+			$post = $this->fetcher->get( $post_id );
+
+			if ( ! $post ) {
+				WP_CLI::warning( "Could not find the post with ID {$post_id}." );
+				++$errors;
+				continue;
+			}
+
+			if ( '' === trim( (string) $post->post_content ) ) {
+				WP_CLI::warning( "Post {$post->ID} has no content to convert." );
+				++$skips;
+				continue;
+			}
+
+			if ( Block_Processor_Helper::has_blocks( $post->post_content ) ) {
+				WP_CLI::warning( "Post {$post->ID} already contains blocks." );
+				++$skips;
+				continue;
+			}
+
+			$markup = gutenberg_html_to_block_markup( $post->post_content );
+
+			if ( $dry_run ) {
+				WP_CLI::log( "Would convert post {$post->ID}." );
+				++$successes;
+				continue;
+			}
+
+			$result = wp_update_post(
+				[
+					'ID'           => $post->ID,
+					'post_content' => $markup,
+				],
+				true
+			);
+
+			if ( is_wp_error( $result ) ) {
+				WP_CLI::warning( "Failed converting post {$post->ID}: " . $result->get_error_message() );
+				++$errors;
+				continue;
+			}
+
+			WP_CLI::log( "Converted post {$post->ID}." );
+			++$successes;
+		}
+
+		if ( ! $dry_run ) {
+			Utils\report_batch_operation_results( 'post', 'convert', $total, $successes, $errors, $skips );
+			return;
+		}
+
+		$skipped_message = $skips ? " ({$skips} skipped)" : '';
+
+		if ( $errors ) {
+			$failed_skipped_message = " ({$errors} failed" . ( $skips ? ", {$skips} skipped" : '' ) . ')';
+			if ( $successes ) {
+				WP_CLI::error( "Would only convert {$successes} of {$total} posts{$failed_skipped_message}." );
+			}
+			WP_CLI::error( "No posts would be converted{$failed_skipped_message}." );
+		}
+
+		WP_CLI::success( "Would convert {$successes} of {$total} posts{$skipped_message}." );
+	}
+
 	/**
 	 * Convert a date-time string with a hyphen separator to a space separator.
 	 *