Her career in the theatre has included parts in Royal Court Theatre and National Theatre productions. In 2007 she played Phoebe Rice in an acclaimed revival of John Osborne's" The Entertainer" at London's Old Vic Theatre. In 2007, Ferris took part in the BBC Wales programme "Coming Home" about her Welsh family history. In 2008 she played Mrs General in an all-star cast BBC adaptation of the Charles Dickens novel "Little Dorrit". From 2009 to 2010, she appeared in the final series of the BBC comedy "Gavin & Stacey" as Cath Smith. In 2010, she made a guest appearance in the sitcom "Grandma's House". From 2012-2016, Ferris played the part of Sister Evangelina in the series "Call the Midwife". She chose to leave as filming was moved to a different location and the