Formerly, he was an official football player on the B.93 football club. His brother Ken is also a profile player. Marco has been playing football since he was a child.
Ilsø got his first acting role as a fourteen-year-old, playing the lead in the Danish family Christmas series called Mikkel og Guldkorte (Mikkel and the golden card), which aired in 2008. In 2011, he also acted in the drama Frit fald (Free Fall) in which he played Niclast, the main character's boyfriend. In 2014, he appeared in Dannys dommedag (Danny's Doomsday) and in the thriller Fasandræberne (The Absent One), playing a young Ditlev, who was played by Pilou Asbæk.