Wynter was born as Dagmar Winter in Berlin, Germany, the daughter of Dr. Peter Wynter (né Winter), who was a noted British surgeon, and his wife, Jutta Oarda, who was Hungarian. She grew up in England.

When young Dagmar was sixteen years old her father travelled to Morocco to operate on a woman who would not allow anyone else to attend her.[citation needed] He visited friends in Southern Rhodesia, fell in love with it and brought his daughter and her stepmother to live with him there.[citation needed]

Dana Wynter (as she called herself) would later enroll at South Africa's Rhodes University (the only female in a class of 150[citation needed]) and dabbled in theatre, playing the blind girl in a school production of Through a Glass Darkly, in which she says she was "terrible". After a year-plus of studies, she returned to England and shifted gears, dropping her medical studies and turning to an acting career. Her film name, Dana, is pronounced "Donna".

Wynter began her cinema career in 1951 by playing small roles, usually uncredited, in British films. One such was Lady Godiva Rides Again (1951) in which other future leading ladies, Kay Kendall, Diana Dors and Joan Collins played similarly small roles. She was appearing in the play Hammersmith when an American agent told her he wanted to represent her. She was again uncredited when she played Morgan Le Fay's servant in the MGM film, Knights of the Round Table (1953).

Wynter left for New York on the 5th of November 1953, Guy Fawkes Day, commemorating an attempt in 1605 to blow up the Parliament building. "There were all sorts of fireworks going off" she later told an interviewer, "and I couldn't help thinking it was a fitting send-off for my departure to the New World".

Wynter had more success in New York than in London. She appeared on the stage and on TV, where she had leading roles in Robert Montgomery Presents (1953), Suspense (1954, with Otto Preminger) and Studio One (1955, with Barry Sullivan), among others. She then moved west to Hollywood where, in 1955, she was placed under contract by 20th Century Fox. In that same year, she won the Golden Globe award for Most Promising Newcomer, a title she shared with Anita Ekberg and Victoria Shaw. Wynter graduated to playing major roles in major films. In 1956 she co-starred with Kevin McCarthy, Larry Gates, and Carolyn Jones, playing "Becky Driscoll", in the original film version of Invasion of the Body Snatchers (1956).

She starred opposite Robert Taylor in D-Day the Sixth of June (1956), alongside Rock Hudson and Sidney Poitier in Something of Value (1957), Mel Ferrer in Fräulein (1958), Robert Wagner in In Love and War (1958), James Cagney and Don Murray in Shake Hands with the Devil (1959), Kenneth More in Sink the Bismarck (1960) and Danny Kaye in On the Double (1961) and The List of Adrian Messenger (1963).

Over the following twenty years, she appeared as a guest star in literally dozens of television series and in occasional cameo roles in films such as Airport (1970). In 1966-67, she co-starred with Robert Lansing on the TV series The Man Who Never Was, but the series lasted only one season. She went on to appear in an Irish soap opera, Bracken (which also starred a young Gabriel Byrne) from 1978-80. In 1993, she returned to TV to play Raymond Burr's wife in The Return of Ironside.

Wynter divorced her only husband, celebrity attorney Greg Bautzer, in 1981. She and Bautzer had one child: Mark Ragan Bautzer, born on January 29, 1960. Wynter, once called Hollywood's "oasis of elegance", now divides her time between homes in California and County Wicklow, Ireland.