Mark Duplass has written, directed, and produced several feature films with his brother Jay Duplass. In 2005, he wrote and produced The Puffy Chair with his brother, in addition to portraying one of the main characters.

The two brothers later wrote, directed, and produced the films Baghead (2008) and Cyrus (2010) together and have a unique style which consists of a great deal of ad-libbing off of the original script, shooting a number of takes, and editing scenes down 15 to 20 times.

Their films Jeff, Who Lives at Home and The Do-Deca-Pentathlon were released in 2012. In 2015, Duplass co-starred with Evan Peters and Olivia Wilde in David Gelb's thriller film The Lazarus Effect.

Currently, he is appearing in the HBO series Togetherness,which he also created.