diff --git a/packages/block-library/src/post-author/block.json b/packages/block-library/src/post-author/block.json
index 6a59b0fe5f1b32..dd7a983f9761cc 100644
--- a/packages/block-library/src/post-author/block.json
+++ b/packages/block-library/src/post-author/block.json
@@ -6,10 +6,12 @@
 			"type": "string"
 		},
 		"avatarSize": {
-			"type": "number"
+			"type": "number",
+			"default": 48
 		},
 		"showAvatar": {
-			"type": "boolean"
+			"type": "boolean",
+			"default": true
 		},
 		"showBio": {
 			"type": "boolean"
@@ -35,6 +37,7 @@
 		"postId"
 	],
 	"supports": {
-		"html": false
+		"html": false,
+		"__experimentalFontSize": true
 	}
 }
diff --git a/packages/block-library/src/post-author/edit.js b/packages/block-library/src/post-author/edit.js
index e45932907251ff..a9d5a66eb07089 100644
--- a/packages/block-library/src/post-author/edit.js
+++ b/packages/block-library/src/post-author/edit.js
@@ -1,37 +1,28 @@
 /**
  * External dependencies
  */
-import { forEach } from 'lodash';
+import { forEach, groupBy } from 'lodash';
 import classnames from 'classnames';
 
 /**
  * WordPress dependencies
  */
-import { useRef } from '@wordpress/element';
+import { useRef, useMemo } from '@wordpress/element';
 import {
 	AlignmentToolbar,
 	BlockControls,
-	FontSizePicker,
 	InspectorControls,
 	RichText,
 	__experimentalUseColors,
 	BlockColorsStyleSelector,
-	withFontSizes,
 } from '@wordpress/block-editor';
 import { PanelBody, SelectControl, ToggleControl } from '@wordpress/components';
 import { useSelect, useDispatch } from '@wordpress/data';
 import { __ } from '@wordpress/i18n';
 
-const DEFAULT_AVATAR_SIZE = 24;
+const DEFAULT_CONTRAST_CHECK_FONT_SIZE = 12;
 
-function PostAuthorEdit( {
-	isSelected,
-	fontSize,
-	setFontSize,
-	context,
-	attributes,
-	setAttributes,
-} ) {
+function PostAuthorEdit( { isSelected, context, attributes, setAttributes } ) {
 	const { postType, postId } = context;
 
 	const { authorId, authorDetails, authors } = useSelect(
@@ -56,6 +47,26 @@ function PostAuthorEdit( {
 
 	const { editEntityRecord } = useDispatch( 'core' );
 
+	// Need font size in number form for named presets to be used in contrastCheckers.
+	const { fontSizes } = useSelect( ( select ) =>
+		select( 'core/block-editor' ).getSettings()
+	);
+	const fontSizeIndex = useMemo( () => groupBy( fontSizes, 'slug' ), [
+		fontSizes,
+	] );
+	const contrastCheckFontSize = useMemo(
+		() =>
+			// Custom size if set.
+			attributes.style?.typography?.fontSize ||
+			// Size of preset/named value if set.
+			fontSizeIndex[ attributes.fontSize ]?.[ 0 ].size ||
+			DEFAULT_CONTRAST_CHECK_FONT_SIZE,
+		[
+			attributes.style?.typography?.fontSize,
+			attributes.fontSize,
+			fontSizeIndex,
+		]
+	);
 	const ref = useRef();
 	const {
 		TextColor,
@@ -72,7 +83,7 @@ function PostAuthorEdit( {
 				{
 					backgroundColor: true,
 					textColor: true,
-					fontSize: fontSize.size,
+					fontSize: contrastCheckFontSize,
 				},
 			],
 			colorDetector: { targetRef: ref },
@@ -80,7 +91,7 @@ function PostAuthorEdit( {
 				initialOpen: true,
 			},
 		},
-		[ fontSize.size ]
+		[ contrastCheckFontSize ]
 	);
 
 	const { align, showAvatar, showBio, byline } = attributes;
@@ -95,17 +106,13 @@ function PostAuthorEdit( {
 		} );
 	}
 
-	let avatarSize = DEFAULT_AVATAR_SIZE;
-	if ( !! attributes.avatarSize ) {
-		avatarSize = attributes.avatarSize;
-	}
-
-	const blockClassNames = classnames( 'wp-block-post-author', {
-		[ fontSize.class ]: fontSize.class,
-	} );
-	const blockInlineStyles = {
-		fontSize: fontSize.size ? fontSize.size + 'px' : undefined,
-	};
+	const classNames = useMemo( () => {
+		return {
+			block: classnames( 'wp-block-post-author', {
+				[ `has-text-align-${ align }` ]: align,
+			} ),
+		};
+	}, [ align ] );
 
 	return (
 		<>
@@ -153,12 +160,6 @@ function PostAuthorEdit( {
 						}
 					/>
 				</PanelBody>
-				<PanelBody title={ __( 'Text settings' ) }>
-					<FontSizePicker
-						value={ fontSize.size }
-						onChange={ setFontSize }
-					/>
-				</PanelBody>
 			</InspectorControls>
 
 			{ InspectorControlsColorPanel }
@@ -180,19 +181,15 @@ function PostAuthorEdit( {
 
 			<TextColor>
 				<BackgroundColor>
-					<div
-						ref={ ref }
-						className={ classnames( blockClassNames, {
-							[ `has-text-align-${ align }` ]: align,
-						} ) }
-						style={ blockInlineStyles }
-					>
+					<div ref={ ref } className={ classNames.block }>
 						{ showAvatar && authorDetails && (
 							<div className="wp-block-post-author__avatar">
 								<img
-									width={ avatarSize }
+									width={ attributes.avatarSize }
 									src={
-										authorDetails.avatar_urls[ avatarSize ]
+										authorDetails.avatar_urls[
+											attributes.avatarSize
+										]
 									}
 									alt={ authorDetails.name }
 								/>
@@ -205,12 +202,6 @@ function PostAuthorEdit( {
 									className="wp-block-post-author__byline"
 									multiline={ false }
 									placeholder={ __( 'Write byline …' ) }
-									withoutInteractiveFormatting
-									allowedFormats={ [
-										'core/bold',
-										'core/italic',
-										'core/strikethrough',
-									] }
 									value={ byline }
 									onChange={ ( value ) =>
 										setAttributes( { byline: value } )
@@ -221,7 +212,7 @@ function PostAuthorEdit( {
 								{ authorDetails?.name }
 							</p>
 							{ showBio && (
-								<p className={ 'wp-block-post-author__bio' }>
+								<p className="wp-block-post-author__bio">
 									{ authorDetails?.description }
 								</p>
 							) }
@@ -233,4 +224,4 @@ function PostAuthorEdit( {
 	);
 }
 
-export default withFontSizes( 'fontSize' )( PostAuthorEdit );
+export default PostAuthorEdit;
diff --git a/packages/block-library/src/post-author/editor.scss b/packages/block-library/src/post-author/editor.scss
index 65c919a25155cd..e57cb18ae23680 100644
--- a/packages/block-library/src/post-author/editor.scss
+++ b/packages/block-library/src/post-author/editor.scss
@@ -1,34 +1,36 @@
-.block-editor__container .wp-block-post-author {
+.wp-block-post-author {
 	display: flex;
 	flex-wrap: wrap;
 	line-height: 1.5;
-}
 
-.wp-block-post-author__byline {
-	color: $dark-gray-300;
-	font-size: $default-font-size;
-	margin-top: 0;
-	position: relative;
-	font-style: normal;
-}
+	.wp-block-post-author__byline {
+		font-size: 0.5em;
+		margin-top: 0;
+		position: relative;
+		font-style: normal;
+	}
 
-.wp-block-post-author__content {
-	flex-grow: 1;
-	flex-basis: 0;
-}
+	.wp-block-post-author__content {
+		flex-grow: 1;
+		flex-basis: 0;
+	}
 
-.block-editor__container .wp-block-post-author__avatar img {
-	margin: 0;
-}
+	.wp-block-post-author__avatar img {
+		margin: 0;
+	}
 
-.block-editor__container .wp-block-post-author__name {
-	margin: 0;
-	margin-top: -$grid-unit-20/2;
-	margin-bottom: -$grid-unit-20/2;
-	font-weight: bold;
-}
+	.wp-block-post-author__avatar {
+		// To fix unknown space added in editor
+		margin-bottom: -$grid-unit-10;
+	}
+
+	.wp-block-post-author__name {
+		margin: 0;
+		font-weight: bold;
+	}
 
-.block-editor__container .wp-block-post-author__bio {
-	margin: 0;
-	margin-top: $grid-unit-20;
+	.wp-block-post-author__bio {
+		margin: 0 0 $grid-unit-10;
+		font-size: 0.7em;
+	}
 }
diff --git a/packages/block-library/src/post-author/index.php b/packages/block-library/src/post-author/index.php
index 111926ed1590ba..2a96766c5b6bdd 100644
--- a/packages/block-library/src/post-author/index.php
+++ b/packages/block-library/src/post-author/index.php
@@ -13,7 +13,11 @@
  * @return array Colors CSS classes and inline styles.
  */
 function post_author_build_css_colors( $attributes ) {
-	$colors = array(
+	$text_colors       = array(
+		'css_classes'   => array(),
+		'inline_styles' => '',
+	);
+	$background_colors = array(
 		'css_classes'   => array(),
 		'inline_styles' => '',
 	);
@@ -25,15 +29,15 @@ function post_author_build_css_colors( $attributes ) {
 	// If has text color.
 	if ( $has_custom_text_color || $has_named_text_color ) {
 		// Add has-text-color class.
-		$colors['css_classes'][] = 'has-text-color';
+		$text_colors['css_classes'][] = 'has-text-color';
 	}
 
 	if ( $has_named_text_color ) {
 		// Add the color class.
-		$colors['css_classes'][] = sprintf( 'has-%s-color', $attributes['textColor'] );
+		$text_colors['css_classes'][] = sprintf( 'has-%s-color', $attributes['textColor'] );
 	} elseif ( $has_custom_text_color ) {
 		// Add the custom color inline style.
-		$colors['inline_styles'] .= sprintf( 'color: %s;', $attributes['customTextColor'] );
+		$text_colors['inline_styles'] .= sprintf( 'color: %s;', $attributes['customTextColor'] );
 	}
 
 	// Background color.
@@ -43,18 +47,21 @@ function post_author_build_css_colors( $attributes ) {
 	// If has background color.
 	if ( $has_custom_background_color || $has_named_background_color ) {
 		// Add has-background-color class.
-		$colors['css_classes'][] = 'has-background-color';
+		$background_colors['css_classes'][] = 'has-background-color';
 	}
 
 	if ( $has_named_background_color ) {
 		// Add the background-color class.
-		$colors['css_classes'][] = sprintf( 'has-%s-background-color', $attributes['backgroundColor'] );
+		$background_colors['css_classes'][] = sprintf( 'has-%s-background-color', $attributes['backgroundColor'] );
 	} elseif ( $has_custom_background_color ) {
 		// Add the custom background-color inline style.
-		$colors['inline_styles'] .= sprintf( 'background-color: %s;', $attributes['customBackgroundColor'] );
+		$background_colors['inline_styles'] .= sprintf( 'background-color: %s;', $attributes['customBackgroundColor'] );
 	}
 
-	return $colors;
+	return array(
+		'text'       => $text_colors,
+		'background' => $background_colors,
+	);
 }
 
 /**
@@ -72,14 +79,16 @@ function post_author_build_css_font_sizes( $attributes ) {
 	);
 
 	$has_named_font_size  = array_key_exists( 'fontSize', $attributes );
-	$has_custom_font_size = array_key_exists( 'customFontSize', $attributes );
+	$has_custom_font_size = array_key_exists( 'style', $attributes )
+	&& array_key_exists( 'typography', $attributes['style'] )
+	&& array_key_exists( 'fontSize', $attributes['style']['typography'] );
 
 	if ( $has_named_font_size ) {
 		// Add the font size class.
 		$font_sizes['css_classes'][] = sprintf( 'has-%s-font-size', $attributes['fontSize'] );
 	} elseif ( $has_custom_font_size ) {
 		// Add the custom font size inline style.
-		$font_sizes['inline_styles'] = sprintf( 'font-size: %spx;', $attributes['customFontSize'] );
+		$font_sizes['inline_styles'] = sprintf( 'font-size: %spx;', $attributes['style']['typography']['fontSize'] );
 	}
 
 	return $font_sizes;
@@ -88,9 +97,9 @@ function post_author_build_css_font_sizes( $attributes ) {
 /**
  * Renders the `core/post-author` block on the server.
  *
- * @param array    $attributes Block attributes.
- * @param string   $content    Block default content.
- * @param WP_Block $block      Block instance.
+ * @param  array    $attributes Block attributes.
+ * @param  string   $content    Block default content.
+ * @param  WP_Block $block      Block instance.
  * @return string Returns the rendered author block.
  */
 function render_block_core_post_author( $attributes, $content, $block ) {
@@ -112,26 +121,32 @@ function render_block_core_post_author( $attributes, $content, $block ) {
 	$colors     = post_author_build_css_colors( $attributes );
 	$font_sizes = post_author_build_css_font_sizes( $attributes );
 	$classes    = array_merge(
-		$colors['css_classes'],
+		$colors['background']['css_classes'],
 		$font_sizes['css_classes'],
 		array( 'wp-block-post-author' ),
 		isset( $attributes['className'] ) ? array( $attributes['className'] ) : array(),
 		isset( $attributes['itemsJustification'] ) ? array( 'items-justified-' . $attributes['itemsJustification'] ) : array(),
-		isset( $attributes['align'] ) ? array( 'align' . $attributes['align'] ) : array()
+		isset( $attributes['align'] ) ? array( 'has-text-align-' . $attributes['align'] ) : array()
 	);
 
 	$class_attribute = sprintf( ' class="%s"', esc_attr( implode( ' ', $classes ) ) );
-	$style_attribute = ( $colors['inline_styles'] || $font_sizes['inline_styles'] )
-		? sprintf( ' style="%s"', esc_attr( $colors['inline_styles'] ) . esc_attr( $font_sizes['inline_styles'] ) )
-		: '';
+	$style_attribute = ( $colors['background']['inline_styles'] || $font_sizes['inline_styles'] )
+	? sprintf( ' style="%s"', esc_attr( $colors['background']['inline_styles'] ) . esc_attr( $font_sizes['inline_styles'] ) )
+	: '';
+
+	// Add text colors on content for higher specificty.  Prevents theme override for has-background-color.
+	$content_class_attribute = sprintf( ' class="wp-block-post-author__content %s"', esc_attr( implode( ' ', $colors['text']['css_classes'] ) ) );
+	$content_style_attribute = ( $colors['text']['inline_styles'] )
+	? sprintf( ' style="%s"', esc_attr( $colors['text']['inline_styles'] ) )
+	: '';
 
 	return sprintf( '<div %1$s %2$s>', $class_attribute, $style_attribute ) .
-		( ! empty( $attributes['showAvatar'] ) ? '<div class="wp-block-post-author__avatar">' . $avatar . '</div>' : '' ) .
-		'<div class="wp-block-post-author__content">' .
-			( ! empty( $byline ) ? '<p class="wp-block-post-author__byline">' . $byline . '</p>' : '' ) .
-			'<p class="wp-block-post-author__name">' . get_the_author_meta( 'display_name', $author_id ) . '</p>' .
-			( ! empty( $attributes['showBio'] ) ? '<p class="wp-block-post-author__bio">' . get_the_author_meta( 'user_description', $author_id ) . '</p>' : '' ) .
-		'</div>' .
+	( ! empty( $attributes['showAvatar'] ) ? '<div class="wp-block-post-author__avatar">' . $avatar . '</div>' : '' ) .
+	sprintf( '<div %1$s %2$s>', $content_class_attribute, $content_style_attribute ) .
+	( ! empty( $byline ) ? '<p class="wp-block-post-author__byline">' . $byline . '</p>' : '' ) .
+	'<p class="wp-block-post-author__name">' . get_the_author_meta( 'display_name', $author_id ) . '</p>' .
+	( ! empty( $attributes['showBio'] ) ? '<p class="wp-block-post-author__bio">' . get_the_author_meta( 'user_description', $author_id ) . '</p>' : '' ) .
+	'</div>' .
 	'</div>';
 }
 
diff --git a/packages/block-library/src/post-author/style.scss b/packages/block-library/src/post-author/style.scss
index 86df3428831421..53fe560773d7a6 100644
--- a/packages/block-library/src/post-author/style.scss
+++ b/packages/block-library/src/post-author/style.scss
@@ -7,7 +7,7 @@
 		width: 100%;
 		margin-top: 0;
 		margin-bottom: 0;
-		font-size: 0.8em;
+		font-size: 0.5em;
 	}
 
 	&__avatar {
@@ -15,7 +15,8 @@
 	}
 
 	&__bio {
-		margin-top: $grid-unit-10;
+		margin-bottom: $grid-unit-10;
+		font-size: 0.7em;
 	}
 
 	&__content {
diff --git a/packages/e2e-tests/fixtures/blocks/core__post-author.json b/packages/e2e-tests/fixtures/blocks/core__post-author.json
index f780184a547e9c..b5f4fcb918a997 100644
--- a/packages/e2e-tests/fixtures/blocks/core__post-author.json
+++ b/packages/e2e-tests/fixtures/blocks/core__post-author.json
@@ -3,7 +3,10 @@
         "clientId": "_clientId_0",
         "name": "core/post-author",
         "isValid": true,
-        "attributes": {},
+        "attributes": {
+			"avatarSize": 48,
+			"showAvatar": true
+		},
         "innerBlocks": [],
         "originalContent": ""
     }