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, for 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 starred in the horror film Creep (2014) and its sequel Creep 2 (2017), as well as the television spin-off The Creep Tapes (2024). He co-wrote and co-produced the television anthology series Room 104 (2017–2020). His other acting credits include Humpday (2009), The League (2009–2015), Greenberg (2010), Safety Not Guaranteed (2012), The One I Love (2014), The Lazarus Effect (2015), Togetherness (2015–2016), Blue Jay (2016), Tully (2018), Goliath (2018–2019), Paddleton (2019), and Language Lessons (2021).