diff --git a/package.json b/package.json
index d680c53851..ce21d01bc7 100644
--- a/package.json
+++ b/package.json
@@ -170,8 +170,8 @@
 		"env:cli": "node ./tools/local-env/scripts/docker.js run cli",
 		"env:logs": "node ./tools/local-env/scripts/docker.js logs",
 		"env:pull": "node ./tools/local-env/scripts/docker.js pull",
-		"test:php": "node ./tools/local-env/scripts/docker.js run --rm phpunit phpunit",
-		"test:php-composer": "node ./tools/local-env/scripts/docker.js run --rm phpunit php ./vendor/bin/phpunit",
+		"test:php": "node ./tools/local-env/scripts/docker.js run -T php composer update -W && node ./tools/local-env/scripts/docker.js run --rm phpunit phpunit",
+		"test:php-composer": "node ./tools/local-env/scripts/docker.js run -T php composer update -W && node ./tools/local-env/scripts/docker.js run --rm phpunit php ./vendor/bin/phpunit",
 		"test:e2e": "node ./tests/e2e/run-tests.js",
 		"wp-packages-update": "wp-scripts packages-update"
 	}
diff --git a/tools/local-env/scripts/install.js b/tools/local-env/scripts/install.js
index 4a21b99953..762273598e 100644
--- a/tools/local-env/scripts/install.js
+++ b/tools/local-env/scripts/install.js
@@ -22,6 +22,8 @@ renameSync( 'src/wp-config.php', 'wp-config.php' );
 
 install_wp_importer();
 
+install_composer_dependencies();
+
 // Read in wp-tests-config-sample.php, edit it to work with our config, then write it to wp-tests-config.php.
 const testConfig = readFileSync( 'wp-tests-config-sample.php', 'utf8' )
 	.replace( 'youremptytestdbnamehere', 'wordpress_develop_tests' )
@@ -57,3 +59,10 @@ function install_wp_importer() {
 	execSync( `docker-compose exec -T php rm -rf ${testPluginDirectory}`, { stdio: 'inherit' } );
 	execSync( `docker-compose exec -T php git clone https://github.com/WordPress/wordpress-importer.git ${testPluginDirectory} --depth=1`, { stdio: 'inherit' } );
 }
+
+/**
+ * Installs the Composer package dependencies within the Docker environment.
+ */
+function install_composer_dependencies() {
+	execSync( `docker-compose run -T php composer update -W`, { stdio: 'inherit' } );
+}