Zeffira was working as an opera singer and classical musician when she first met Badwan. The two friends began to write songs together and formed the band Cat's Eyes. The duo made their first public appearance at The Vatican, where they performed one of their songs as a mass setting, with organ and choir during a service at St. Peter's Basilica. Cat's Eyes was signed by Polydor in 2010 and released their eponymous debut album in April 2011. The album received positive press and critical acclaim. During this time, Zeffira appeared in Vogue magazine, and was shot by the photographer Ian Rankin for the cover of Dazed & Confused alongside Bobby Gillespie of Primal Scream.
Zeffira's first solo album, The Deserters, was released 10 December 2012 on RAF Records in Europe and Paper Bag Records in North America. The title track was chosen for the trailer to the final season of the TV program Skins. Zeffira received positive press for the debutand the album was listed in The Times Top 5 albums of 2012 in spite of its late release date.
Zeffira also received critical praise for her live performances.In June 2013. she was the opening act for Glastonbury Festival 2013.
Zeffira is listed as composer, arranger, orchestrator, conductor, musician and soprano on Cat's Eyes soundtrack for the 2014 film The Duke of Burgundy, directed by Peter Strickland. The score received positive press and majority 5 star reviews  On 7 November 2015 it was announced that Zeffira and Badwan had won the European Film Award for Best Composer.