diff --git a/themes/osi/functions.php b/themes/osi/functions.php
index 3be3513..698093b 100755
--- a/themes/osi/functions.php
+++ b/themes/osi/functions.php
@@ -294,6 +294,11 @@ function osi_add_block_editor_assets() {
  */
 require get_template_directory() . '/inc/megamenu-featured.php';
 
+/**
+ * Mobile menu CTA field.
+ */
+require get_template_directory() . '/inc/menu-cta.php';
+
 /**
  * Color functions.
  */
diff --git a/themes/osi/header-ai.php b/themes/osi/header-ai.php
index 0f0442a..77d8e15 100755
--- a/themes/osi/header-ai.php
+++ b/themes/osi/header-ai.php
@@ -50,7 +50,12 @@
 							);
 					endif;
 					?>
-					<a class="nav-main--cta" href="<?php echo esc_url( home_url( '/get-involved/' ) ); ?>"><?php esc_html_e( 'Get Involved', 'osi' ); ?></a>
+					<?php
+					$osi_cta = osi_menu_cta();
+					if ( null !== $osi_cta ) {
+						echo '<a class="nav-main--cta" href="' . esc_url( $osi_cta['url'] ) . '"' . ( $osi_cta['target'] ? ' target="_blank" rel="noopener noreferrer"' : '' ) . '>' . esc_html( $osi_cta['label'] ) . '</a>';
+					}
+					?>
 				</nav><!-- #site-navigation -->
 
 				<section class="open-button-wrapper">
diff --git a/themes/osi/header.php b/themes/osi/header.php
index 79406b3..9a933dd 100755
--- a/themes/osi/header.php
+++ b/themes/osi/header.php
@@ -61,7 +61,12 @@
 						);
 					endif;
 					?>
-					<a class="nav-main--cta" href="<?php echo esc_url( home_url( '/get-involved/' ) ); ?>"><?php esc_html_e( 'Get Involved', 'osi' ); ?></a>
+					<?php
+					$osi_cta = osi_menu_cta();
+					if ( null !== $osi_cta ) {
+						echo '<a class="nav-main--cta" href="' . esc_url( $osi_cta['url'] ) . '"' . ( $osi_cta['target'] ? ' target="_blank" rel="noopener noreferrer"' : '' ) . '>' . esc_html( $osi_cta['label'] ) . '</a>';
+					}
+					?>
 				</nav><!-- #site-navigation -->
 				<section class="open-search-wrapper">
 				<a aria-label="Open Search" class="open-search open-button jetpack-search-filter__link" href="#">
diff --git a/themes/osi/inc/menu-cta.php b/themes/osi/inc/menu-cta.php
new file mode 100644
index 0000000..e19ee98
--- /dev/null
+++ b/themes/osi/inc/menu-cta.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * Mobile menu CTA: field registration + resolution.
+ *
+ * @package osi
+ */
+
+add_action( 'acf/include_fields', 'osi_menu_cta_field' );
+/**
+ * Register the CTA link field shown on the primary menu's settings in Appearance > Menus.
+ *
+ * @return void
+ */
+function osi_menu_cta_field() {
+	acf_add_local_field_group(
+		array(
+			'key'             => 'group_osi_menu_cta',
+			'title'           => __( 'Mobile menu CTA', 'osi' ),
+			'label_placement' => 'top',
+			'fields'          => array(
+				array(
+					'key'           => 'field_osi_menu_cta_link',
+					'label'         => __( 'CTA link', 'osi' ),
+					'name'          => 'osi_menu_cta_link',
+					'type'          => 'link',
+					'instructions'  => __( 'Bottom button of the mobile menu only. Empty = no button.', 'osi' ),
+					'return_format' => 'array',
+				),
+			),
+			'location'        => array(
+				array(
+					array(
+						'param'    => 'nav_menu',
+						'operator' => '==',
+						'value'    => 'location/primary_navigation',
+					),
+				),
+			),
+		)
+	);
+}
+
+/**
+ * Resolve the mobile menu CTA; no field value means no button.
+ *
+ * @return array|null Array with 'url', 'label' and 'target' (boolean) keys, or null.
+ */
+function osi_menu_cta() {
+	$locations = get_nav_menu_locations();
+	$menu      = function_exists( 'get_field' ) ? wp_get_nav_menu_object( $locations['primary_navigation'] ?? 0 ) : false;
+	$link      = $menu ? (array) get_field( 'osi_menu_cta_link', $menu ) : array();
+	$url       = ! empty( $link['url'] ) ? esc_url_raw( $link['url'] ) : '';
+
+	if ( '' === $url ) {
+		return null;
+	}
+
+	return array(
+		'url'    => $url,
+		'label'  => ! empty( $link['title'] ) ? $link['title'] : __( 'Get Involved', 'osi' ),
+		'target' => ! empty( $link['target'] ),
+	);
+}