[6] In the summer of 2012, his father sent a recording of him singing to an audition, which landed Tønnesen the leading role in a theatre play called Cirkus Summarum.

He resumed his foray into acting in 2018, taking on the role of Rasmus Andersen in the first Netflix Danish series, The Rain at the age of sixteen.

In 2022, he took on a recurring role in a Netflix co-production series, Borgen – Power & Glory, as Magnus Nyborg Christensen.

[5][11] He later starred in the multilingual Netflix mystery-horror series 1899, created by Baran bo Odar and Jantje Friese.

[12][13][14] In 2020, Tønnesen became an ambassador for Emporio Armani in the EA Building Dialogues Fashion Show in Milan.