According to Us Weekly, Kirsten, 33, and Garrett, 31, have called it quits, putting an end to their four-year relationship.
The pair had been dating since meeting on the set of their 2012 film On The Road (based on the Jack Kerouac novel of the same name). They went public as a couple in January 2012 and had been living together in Los Angeles since.
Kirsten, famous for her roles in films such as Little Women and the Spiderman series, was last spotted with her actor boyfriend in January, at the Golden Globes Awards in Beverly Hills, California. The actress had been nominated for a Golden Globe for her portrayal of Peggy Blumquist in season two of the US series Fargo, but lost out to Lady Gaga who starred in the series American Horror Story: Hotel.
The split news comes as a surprise to many, after much speculation that an engagement was on the cards for the Hollywood couple. The actress has spoken openly about her desire to start a family, revealing in an interview with Net-A-Porter that she was hoping to start a family in the not too distant future.
'I want to continue acting, but I also want to have kids,' she said. 'I think I'll be ready to have them in two years or something.' Marriage is something the Bring It On star has also spoken about: 'I am someone who wants to get married. If it happens in my mid-to-late 30s, it's going to be intimate.
'Court house, dinner party and DJ with friends and family. I'll treat it like it would be my 40th birthday.'
Kirsten with ex-boyfriend Jake Gyllenhaal
The reason for the split is not known. Kirsten's past high-profile romances include Razorlight frontman Johnny Borrell and actor Jake Gyllenhaal, as well as being linked to Adam Brody, Ben Foster and Justin Long.