Massey continued to make occasional film and stage appearances, but worked more frequently in television. She made her first small-screen appearance as Jacqueline in Green of the Year in October 1955, and thereafter featured in dramas such as The Pallisers (1974), the 1978 adaptation of Rebecca (in which she starred with her ex-husband Jeremy Brett), The Mayor of Casterbridge (1978), The Cherry Orchard (1980), and Anna Karenina (1985). She had roles in the British comedy series The Darling Buds of May (1991) and The Robinsons (2005). She also appeared in a number of mysteries and thrillers on television, including episodes of Inspector Morse, The Inspector Alleyn Mysteries, Midsomer Murders, Strange, Lewis, and Agatha Christie's Poirot.

Several of her early film roles were in mystery thrillers. She made her cinema debut in the Scotland Yard film Gideon's Day (1958) as Sally, daughter of Jack Hawkins's Detective Inspector. The Director was her godfather John Ford. She played a potential murder victim in Michael Powell's cult thriller Peeping Tom (1960) and appeared in Otto Preminger's Bunny Lake Is Missing (1965). In 1972 she played the role of the barmaid Babs in Alfred Hitchcock's penultimate film Frenzy. In the documentary on the film's DVD release, Massey mentioned that she originally auditioned for the much smaller role of the secretary Monica, a part for which Jean Marsh was cast. She also noted that her character's nude scenes in Frenzy were performed by body doubles. She appeared alongside her brother Daniel—they played siblings—in the horror film The Vault of Horror (1973).

In 1987, Massey was awarded the BAFTA Award for Best Actress for her role in Hotel du Lac after acquiring the TV rights two years earlier, only a few weeks before the novel won the Booker Prize. She also appeared as Mrs. D'Urberville in the 2008 BBC adaptation of Tess of the D'Urbervilles, an older version of May and as Rosie in An Angel For May, and in the 2004 BBC version of Our Mutual Friend.

In the New Year's Honours List published on 31 December 2004, she was created a Commander of the Order of the British Empire (CBE) for services to drama.

Massey published an autobiography in 2006, Telling Some Tales, in which she revealed a difficult early life and discussed her failed marriage (1958–1962) to actor Jeremy Brett, discussing his struggle with bipolar disorder. The couple had one son, Writer and Illustrator David Huggins (b. 1959). At an August 1988 dinner party held at the home of their mutual friend, Joy Whitby, she met Russian-born metallurgist Uri Andres, who had been based at Imperial College, London since 1975. The couple were married from November 1988 until her death in 2011.

With Imelda Staunton, she co-devised and starred as Josephine Daunt in Daunt and Dervish on BBC radio. She was the narrator of This Sceptred Isle on BBC Radio 4, a history of Britain from Roman times which ran for more than 300 fifteen-minute episodes. In 2009, she also appeared in a new radio version of The Killing of Sister George.