Kaas graduated from the National Theater School in Denmark in 1998.

He first appeared on screen in Søren Kragh-Jacobsen's film The Boys from St. Petri in 1991 as Otto, the rebel son of a traitor.

Kaas has hosted the Zulu Comedy Galla [da] on Danish TV three times (2009, 2011, 2012).

[citation needed] Their daughter Gerda Lie Kaas starred in the lead role of Clara for the Danish juvenile fantasy film, Wild Witch (2018).

[2] In 2002 and 2012, Kaas won the Robert Award for Best Actor in a Leading Role.