David McCallum's parents were both members of the London Philharmonic; his mother was a cellist and his father was first violinist. The young Scots-born McCallum himself planned to pursue a musical career after serving with the Royal West African Frontier Force, but decided instead upon acting. Following his studies at the RADA, McCallum entered films in 1957, where he was usually cast as a troublemaking street punk or callow junior officer. His first American film (albeit lensed principally in England) was Freud (1962), in which he played a profoundly mother-obsessed mental patient.
McCallum became the rage of the teeny-bopper set when he was cast as cool-headed Russian secret agent Ilya Kuryakin on TV's The Man From UNCLE (1964-68). At one point, McCallum was receiving far more fan mail than the series' ostensible star, Robert Vaughn; he took advantage of his celebrity to launch a brief singing career, duetting with Nancy Sinatra on the 1966 UNCLE episode "The Take Me to Your Leader Affair." He also wrote the music and lyrics and sang the title song of his 1967 movie vehicle Three Bites of the Apple. Following UNCLE, McCallum had a handful of solid dramatic film roles before returning to the small screen in the short-lived 1975 series The Invisible Man.
He continued to appear primarily in episodic television, although he occasionally could be glimpsed on the big-screen as well. Highlights include The Watcher in the Woods, Matlock, The Wind, Murder She Wrote, and The A-Team. The nineties began with a major part in the sleeper Hear My Song, before continuing in Healer, Law and Order, and Cherry. McCallum became a fixture on television yet again at the beginning of the 21st century when he was cast as Donald "Ducky" Mallard on CBS' drama NCIS, which was for a time the top-rated scripted drama on network television.
A man of sundry outside interests, McCallum's range of expertise includes computers and small-arms weaponry. Once wed to actress Jill Ireland, David McCallum has since 1967 been married to Katherine Carpenter.