O'Sullivan trained at Drama Centre London (now Central Saint Martins). As an actress and singer she has appeared in musicals such as The Rocky Horror Show, playing Magenta/Usherette at London's Piccadilly Theatre, Mistress Dainty in Wycherley's Country Wife adaptation : Lust (Haymarket Theatre) and Barbara in Ray Cooney's classic 1970s farce Run For Your Wife starring Eric Sykes. In 2017, she appeared in the Rose d'Or winning sitcom Henry IX for UKTV Gold, starring Sally Phillips and Charles Edwards. As a writer/performer and impressionist, she has appeared in a variety of TV and radio productions such as BBC's Dead Ringers , co-writing for 2 series of Rory Bremner's Radio 4 satirical take on the world, several Edinburgh shows , cabaret and stand-up with Barry from Watford at London's legendary 100 Club and most recently, going back to her roots as a child impressionist, by impersonating Margaret Thatcher for Classic FM's 25th anniversary celebrations in October 2017. O'Sullivan is a prolific voice artist, and is station voice at Absolute Radio and Magic FM (2009 - present).