According to The Sun, the couple will tie the knot in southern France at the end of this week.
James Righton, from the rock band The Klaxons, proposed to the British actress in 2012 after a relationship of 15 months. Their wedding will take place near Nice.
“Most of their friends will fly out for the wedding on Friday,” a source told The Sun.
“They’ve been planning it for a while but wanted something small and private. They could get married in total private in stunning surroundings.”
The two stars, who moved in together in early 2012, met through a mutual friend, fashion editor Alexa Chung, in January 2011.