Todd made her film debut in Keepers of Youth (1931). She had roles in These Charming People (1931), The Ghost Train (1931), The Water Gipsies (1932) and The Return of Bulldog Drummond (1934).
For Alex Korda, Todd was in Things to Come (1936), Action for Slander (1937), The Squeaker (1937), and South Riding (1938). He appeared in Ann and Harold (1938) the first British TV serial.
Todd was in Poison Pen (1939), Danny Boy (1941), and Ships with Wings (1941).
Todd was off screen for a number of years. She had a good support role in a big hit, Perfect Strangers (1945, as a nurse), then had a huge success when she played a suicidal concert Pianist in The Seventh Veil (1945), opposite James Mason. She followed this with a musical, Gaiety George (1946) and a noir Daybreak (shot in 1946, released in 1948).
She received a Hollywood offer from Alfred Hitchcock to play Gregory Peck's wife in The Paradine Case (1947), which was a flop. So Evil My Love (1948), a US-British co production was a box office disappointment, as was The Passionate Friends (1949), directed by her then husband David Lean.
Todd married film Director Lean on 21 May 1949 and starred in a number of his films, including The Passionate Friends (1949), Madeleine (1950) and The Sound Barrier (1952). Lean and Todd divorced 15 July 1957.
Lean also directed Todd in Madeleine (1950) and The Sound Barrier (1952); the latter was very successful commercially.
Todd appeared in some thrillers, The Green Scarf (1954) and Time Without Pity (1957). She had a good part in Hammer Films' Taste of Fear (1961).
In 1957, Todd starred in the Broadway production of Four Winds.