At age 19, Mattsson moved to Hollywood to audition for a TV series. Her planned short visit became permanent after she won a role for the unsold 2004 TV series pilot
Sweden, Ohio. Mattsson's accent initially held her back: "When I started working, my thick Swedish accent lost me a lot of roles. A defining point in my career definitely came when I started to lose it. I was able to play more American roles at that point, and my career took a turn for the better." In 2007, Mattsson starred in the science fiction action thriller film,
Species: The Awakening, portraying Miranda, an alien/human hybrid. The following year she starred opposite
Mischa Barton in the drama film
You and I about Russian pop-band
t.A.T.u. The film premiered at the
Cannes Film Festival in May 2008 and was released in the United States on 31 January 2012. In 2009 she co-starred in the science fiction action film,
Surrogates. On television, Mattsson made guest appearances on
Two and a Half Men,
Rules of Engagement,
Legend of the Seeker,
NCIS: Los Angeles and
The Mentalist. In 2010, she appeared in a minor role in the superhero film
Iron Man 2 and had a recurring role in the
ABC series
Desperate Housewives as Irina Kosokov. She later had three episode-arc in the CW action series,
Nikita, as Cassandra Ovechkin. In 2012, Mattsson starred alongside
Gary Oldman and
Christian Slater in the action film,
Guns, Girls and Gambling. Later that year, she had a series regular role in the ABC supernatural horror series,
666 Park Avenue. The series was canceled after a single season in 2013. She later had a recurring roles in the ABC series
Betrayal in 2013, and
Mistresses in 2014. Also in 2014, Mattsson appeared in two episodes of FX crime series,
Fargo, and in 2015 played the female lead in the
Hallmark Channel romantic comedy film,
Win, Lose or Love. From 2015 to 2016 she had a recurring role in the FX horror series,
American Horror Story: Hotel. She appeared in a beaver costume in a
Nespresso television commercial titled "Training Day" that also featured
Danny DeVito and
George Clooney in 2016. In 2016, Mattsson starred alongside
Reza Sixo Safai in the action crime film,
The Loner, the film received positive reviews from critics. She later appeared in a number of direct-to-video releases, such as
Code of Honor (2016) and
Smartass (2017). In 2018, Mattsson played Swedish actress and model
Britt Ekland in the HBO biographical drama film
My Dinner with Hervé about
Hervé Villechaize. Also that year, Mattsson starred alongside her younger sister
Sofia in the
Lifetime television thriller film ''My Husband's Secret Wife
. She later appeared in several other Lifetime movies: The Perfect One
(2018), Neighborhood Watch
(2018), Her Deadly Reflections
(2019), Swipe Right, Run Left
(2019), and Murder in the Vineyard
(2020). From 2021 to 2022, Mattsson had a recurring role in the ABC police drama series, The Rookie. In early 2022, she pinch-hit for Sofia in the role of Sasha Gilmore on the ABC daytime soap opera General Hospital''. ==Personal life==