[1] There she acted in several plays such as Byggmästare Solness, Spindelkvinnans kyss, Knäckebröd och hovmästarsås,[1] and Köpmannen i Venedig (The Merchant of Venice).

She appeared in Miffo (2003), Masjävlar (2004), for which she won the Guldbagge Award for Best Actress in a Supporting Role, and also in the film Järnets änglar.

[4][2] In 2016, Ernst played a lead role as Anna Linder in the comedy series Finaste Familjen (My Perfect Family) on TV4.

[6] In 2024 she played Lena Nymark in Season 4 of the TV crime drama series Those Who Kill.

[7] Kajsa Ernst was married to actor and director Göran Stangertz from 2009[1] and until his death in 2012.