Pääkönen was born Helsinki, Finland and he is the son of Finnish actor Seppo Pääkkönen. His first major role was that of Saku Salin in the long running Finnish soap opera Salatut elämät. Following this he starred in Bad Boys, which is was thesecond most successful film in Finland in 2003. This was followed with roles in films such as Private Eye Vares and Frozen Land. In 2006 he played real life ski jumper Matti Nykänen in the biopic Matti: Hell Is for Heroes. Pääkkönen also played the role of Kyynpakkaus in the crime film Vares - Kiss of Evil and several of its seqeuls. He also won the Jussi Award for Best Sipporting actor in 2014 for his role in the critically acclaimed film Heart of a Lion. His performance in this film led him to be cast in the History Channel hit-series Vikings, in which he played Halfdan as a series regular. After leaving Vikings he was cast in the Spike Lee-joint BlacKkKlansman as Felix Kendrickson, a member of the Ku Klux Klan. The film was nominated for several Academy Awards, including Best Picture, Best Director, Best Adapted Screenplay and Best Supporting Actor, from which it won Best Adapted Screenplay. He is set to work again with Spike Lee in the upcoming Netlix Film Da 5 Bloods.