Gustaf is the second oldest child to Stellan and My Skarsgård and has 7 siblings: Alexander, Sam, Bill, Eija, Valter, and half-brothers Ossian and Kolbjorn.
His first acting role was at the age of 9 in Täcknamn Coq Rouge (Code Name: Coq Rouge), in which his father had the lead role. In 1999, he entered The Stockholm Academy of Dramatic Arts (Teaterhögskolan) and graduated in 2003. He joined Dramaten Theatre Company in 2003 and starred in many stage productions such as The Merchant of Venice and Lulu.
While continuing with stage productions, he was also in a number of TV and film roles, most notably Den Osynlige (The Invisible) in 2002 and Oscar-nominated Ondskan (Evil) in 2003. Gustaf received a Best Supporting Role Guldbaggen (Swedish Oscars) nomination for Ondskan. In 2006, he won a Guldbaggen for his role as Johan in Förortsungar (Kidz in Da Hood).
2007 and 2008 have been busy for him, having roles in both of the Arn films (with father Stellan and brothers Bill and Valter) as well as sustaining his on-going love for the stage with the production of Den Allvarsamma Leken (The Serious Game) at Stockholm City Theatre. Most recently starring as Göran Skoogh in Patrik 1,5 (Patrik Age 1.5)
In 2017 he was cast as Karl Strand in HBO's Westworld.