Mark David Duplass (born December 7, 1976) is an American filmmaker, actor, writer, and musician. With his brother Jay Duplass, he started the film production company Duplass Brothers Productions in 1996, in which they wrote and directed The Puffy Chair (2005), Baghead (2008), Cyrus (2010), Jeff, Who Lives at Home (2011), and The Do-Deca-Pentathlon (2012).

Duplass co-wrote and co-produced the television anthology series Room 104 (2017–2020), and co-wrote and starred in the horror film Creep (2014) and its 2017 sequel. His other acting credits include Humpday (2009), The League (2009–2015), Greenberg (2010), The Mindy Project (2012–2014), Safety Not Guaranteed (2012), Tammy (2014), The One I Love (2014), The Lazarus Effect (2015), Togetherness (2015–2016), Blue Jay (2016), Tully (2018), Goliath (2018–2019), Paddleton (2019), Bombshell (2019), and Language Lessons (2021).

For his potryal of Charlie "Chip" Black in The Morning Show (2019–present), Duplass received a nomination for the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series. He was also the lead singer of the indie rock band Volcano, I'm Still Excited!!