Loftus made her mainstream television debut in 2000, when she appeared in an episode of Peak Practice. Subsequently, Loftus has appeared in various television series, including Casualty, Doctors, The Bill, and in the ITV comedy drama The Fattest Man in Britain, starring Timothy Spall and Bobby Ball.
In 2008 Loftus was described as a "star of tomorrow" in Screen International magazine. She also appeared in Daniel Elliott’s short Jade, which won a Silver Bear at the Berlin International Film Festival in 2009.
Loftus played Leonie Fowler in the summer box office hit Spur of the Moment by Anya Reiss at the Royal Court Theatre in 2010 in London where she has received favourable reviews with Dominic Cavendish of The Daily Telegraph calling her "superb." In February 2017, she played Joan in the fortieth anniversary production at Nottingham Playhouse of Touched by Stephen Lowe.
In 2011, Loftus starred in a new BBC TV film version of The Borrowers broadcast on Boxing Day, as Arrietty. This was followed up in 2012 with roles in two BBC series : Jade in Public Enemies and Cassandra in Good Cop and in 2013 by the role of Agnes Towler in ITV's Mr. Selfridge. In 2016, she played Sonya Rostova in the BBC prime-time drama War & Peace.