Newman was born in Northampton, Northamptonshire, England. She was the daughter of a show Business family - her father was reputed to be a circus strongman, and her mother was also in show Business. In the 1940s, she lived in Pullman Court, Streatham Hill. She was educated at Sternhold College, the Italia Conti Academy of Theatre Arts stage school and the Royal Academy of Dramatic Art in London.

Newman made her first screen appearance at age 11 in the 1945 short Here We Come Gathering: A Story of the Kentish Orchards. Her feature film debut as a teenager was in Personal Affairs released in 1953. There followed a number of period roles, including the heroine in The Wrong Box (1966); The Madwoman of Chaillot (1969); The Raging Moon (1971), as a young woman in a wheelchair and International Velvet (1978).

Newman met actor-writer-director Bryan Forbes in February 1954 on location at Marylebone railway shunting yards, while Forbes was co-starring in the film Wheel of Fate. Newman, then still at RADA, had been sent along for a job:

Newman and Forbes married on 27 August 1955, and had two daughters, Emma Forbes and Sarah Standing. They were married for 58 years, until Forbes' death in 2013. In her first interview after Forbes' death, Newman explained that one of the reasons they were able to keep their marriage together was Forbes' rule that he always took his family with him if he was working overseas for any period longer than two weeks.

Newman is from a variety background, acting on stage and also appearing in television advertisements, including for Fairy Liquid. She was also a popular regular panellist on a revival of the BBC panel game show What's My Line? (1973–74).

In his 1983 book Adventures in the Screen Trade, scriptwriter william Goldman was critical of the fact that Forbes cast his wife (then in her early forties) as Carol, one of the robotic spouses in The Stepford Wives, and revealed that it led to a major rift between them. In Goldman's original script (of which, he claimed, about 75% was re-written by Forbes), the android replacement wives were meant to be like (Playboy) "Playmates come to life", the acme of youth and beauty, dressed in skimpy tennis shorts and T-shirts. Although Goldman conceded that Newman was both a good Actress and attractive, she clearly did not fit his conception of the part ("a sex bomb she isn't"), and he objected to Forbes' decision to change the appearance of the 'wives' (making them older, more demure and much more conservatively dressed), expressing the view that Newman's casting "destroyed the reality of a story that was only precariously real to begin with". Goldman also recounted his misgivings about casting an Englishwoman to play an American - although, in the event, Newman delivered a perfect accent, and few viewers would have realised she was not American.

She is the author of thirty children’s books and six cookery books; winning a Cookbook of the Year Award with The Summer Cookbook, and presented a children's television cookery programme, Fun Food Factory (1976).