As a sprinter, Mariën specialized in the 200 metres and won gold in the 4 × 100 m relay at the 2008 Beijing Olympics.

Mariën reached the semi-final at the 2006 European Championships and won the bronze medal at the 2007 Summer Universiade.

At the 2007 World Championships she won a bronze medal in the 4 × 100 m relay, together with teammates Olivia Borlée, Élodie Ouédraogo and Kim Gevaert.

[2] In 2016, after Yuliya Chermoshanskaya's re-tested samples revealed two illegal substances, Russia was disqualified promoting Belgium to first place.

With the national bobsleigh team, she participated at the 2014 Winter Olympics, where she and Elfje Willemsen ended sixth in the two woman bob.