The Onion media bias rating is Lean Left.

The Onion is an American satirical digital media company and newspaper organization that publishes articles on international, national, and local news. The company is based in Chicago but originated as a weekly print publication on August 29, 1988 in Madison, Wisconsin. The Onion began publishing online in the spring of 1996. In 2007, they began publishing satirical news audio and video online as the Onion News Network. In 2013, The Onion ceased publishing its print edition and launched Onion Labs, an advertising agency.
Source: Wikipedia