Donald was born in Aberdeen, the fourth son of a Scottish Presbyterian minister. Hismother died when he was 18 months old and his father remarrried.
Donald grew up in Galasheils and was schooled at Rossall School on Lancashire's Fylde coast. He briefly attended McGill University in Montreal, but his asthma meant he transferred to Edinburgh University.
Donald originally intended to be a teacher by seeing Sir Cedric Hardwicke and Dame Edith Evans in The Late Christopher Bean made him decde to be an actor.
He began seeing as many shows as possible and studied at the London Theatre Studio for two years.
He made his stage debut in 1938 in The White Guard and he began to get work regularly on stage. He appeared in Twelfth Night with Michael Redgrave and understudied John Gielgud in King Lear. He toured the provinces in The Cherry Orchard.
During World War II he played minor roles in several war films, including Alibi (1942), In Which We Serve (1942), Went the Day Well? (1942), San Demetrio London (1943) and The Way Ahead (1944). He achieved fame on stage appearing in Present Laughter by Noel Coward. In 1943 he was signed by MGM.
Donald went into the British Army was assigned to British Army Intelligence where he decoded messages for the Intelligence Corps.
After the war he resumed his career. On stage he was in The Eagle with Two Heads (1947) and You Never Can Tell (1948) In films, MGM loaned him to Gainsborough Studios for Broken Journey (1948). He was in also The Small Voice (1948) and MGM's Edward, My Son (1949).
Donald had a big success on stage in The Heiress (1949) with Ralph Richardson, Peggy Ashcroft and Donald Sinden. It led to Laurence Olivier casting him in a production of Captain Caravallo (1950).
For films, he was Jean Kent's love interest in Trottie True (1949) and supported Jean Kent in Cage of Gold (1950) and Googie Withers in White Corridors (1951).
Donald had the lead in a comedy Brandy for the Parson (1952) and supported Trevor Howard and Richard Attenborough in Gift Horse (1952). He played Mr. Winkle in the 1952 film version of The Pickwick Papers.
He had the lead in The Net (1953) and was cast in his first Hollywood film in MGM's Beau Brummell (1954). The same studio hired him to play Theo Van Gogh in Lust for Life (1956).
He memorably portrayed Major Clipton, the doctor who expresses grave doubts about the sanity of Col. Nicholson's (Alec Guinness) efforts to build the bridge in order to show up his Japanese captors, in the classic war film The Bridge on the River Kwai (1957). He had the honour of speaking the film's iconic final words: "Madness!, Madness!"
Donald was in much demand to play supporting roles in action and/or POW films: The Vikings (1958); Third Man on the Mountain (1959); Group Captain Ramsey, the Senior British Officer in The Great Escape (1963); King Rat (1965), a doctor in a POW camp; and Cast a Giant Shadow (1966). He played a colonel in a comedy The Jokers (1967) and had an excellent part as a heroic scientist in Quatermass and the Pit (1967).
Donald starred in a 1960 television adaptation of A. J. Cronin's The Citadel and appeared regularly in many other television dramas in the UK and US, as well as on stage. In 1961, he played Prince Albert opposite Julie Harris's Queen Victoria, in the Hallmark Hall of Fame production of Laurence Housman's play Victoria Regina, for which he received an Emmy nomination.
He performed Write Me a Murder (1961) on Broadway.
Later film roles included Hannibal Brooks (1969), The Royal Hunt of the Sun (1969), David Copperfield (1969), Conduct Unbecoming (1975) and The Big Sleep (1978).
Donald retired from acting in part because of a lifelong asthmatic condition. He died of stomach cancer on 3 August 1993 in West Tytherley, Hampshire. He was survived by his wife, Ann, and a stepson."White Guard" (1938)
"Swords About the Cross" (1938)
"Weep for the Spring" (1939)
"Twelfth Night" (1939)
"King Lear" (1940)
"Thunder Rock" (1943)
"The Time of Your Life" (1943)
"Present Laughter" (1943)
"This Happy Breed" (1943)
"The Brothers Karamazov" (`946)
"The Eagle Has Two Heads" (1947)
"The Cherry Orchard" (1948)
"You Never Can Tell" (1948)
"The Heriress" (1949)
"Captain Carvallo" (1950)
"Peter Pan" (1952)
"Slightly Soiled" (1953)
"The Dark is Light Enough" (1954)
"The Gates of Summer"(1956)
"Face of a Hero" (1960)
"Write Me a Murder" (1961)
The Wings of the Dove" (1963)
"The Doctor's Dilemma" (1963)
"School for Scandal" (1970)
"The Marquise" (1971)
"Emperor Henry IV" (1973)