Stage

After graduating she made her first stage appearance at the Edinburgh Festival in East and A Clockwork Orange. She then went on to play Laurie in The Traveller at the Leicester Haymarket (1987) which transferred to The Almeida Theatre (1988), Emilie, and later on the role of Madame de Tourvel, in the West End Production of Les Liaisons Dangereuses at the Ambassadors Theatre (1989), Yelena in Marya at the Old Vic directed by Roger Michell (1990), Ellen in "Acid Hearts" at the Finborough Theatre (1992), Emma in Betrayal at the Chester Gateway Theatre (1994).

In July 2011, Helen Masters returned to the stage to play the role of Lady Magdalene Danvers in Into Thy Hands, a new play written and directed by Jonathan Holmes at Wiltons Music Hall, London.

In March 2011, Masters played Molly in Revolution Square at the Bush Theatre, London, again written and directed by Jonathan Holmes.

Television

Masters's work in television increased during the early 1990s, culminating in her portrayal of D.I. Lucy Lane in the HTV television series Wycliffe from 1994 to 1998. The series starred Jack Shepherd as Det. Superintendent Wycliffe and Jimmy Yuill as D.I. Doug Kersey.