Mortimer played an aspiring Actress opposite Andy García in City Island (2009) and as Rachel Solando in Martin Scorsese's 2010 film Shutter Island. She played Leonie Gilmour in Leonie, released in the autumn of 2010. In 2011, she had a role in Our Idiot Brother as Liz, the sister of Paul Rudd's character. Also in 2011, she started work with the acclaimed Screenwriter and Producer Aaron Sorkin as Mackenzie McHale in HBO's The Newsroom. In January 2013 it was announced that Mortimer would be co-creating and starring in the comedy series Doll & Em for Sky Living, along with her longtime friend, Actress and Comedian Dolly Wells.