[1] Janssens studied under Guido Henderickx at Studio Herman Teirlinck in Antwerp, graduating in 2003.

[1] In 2006, at age 27, Janssens played the lead role in the film (and preceding television series), King of the World, which was shot in Cuba; he also starred in Hans Herbots' Stormforce that was released in that year.

[6] In 2022, Janssens played Peter, Rémi's father, in Lukas Dhont's Close, which won Grand Prix at the 75th Festival de Cannes,[7] and was nominated for Best International Feature Film at the 95th Academy Awards.

[8] Janssens' stage work includes his 2007 appearance and touring in a production of Pushkin’s Eugene Onegin.

[10][11] An image of Janssens shot with a Nikon D850 by Pieter Clicteur during Filmfestival Oostende was a submission to the 17th Annual Smithsonian Magazine Photo Contest.