At 19 years old, Langton left the theatre and went to live on Yell, a remote island in Shetland, and became a sheep farmer while attempting to become a writer.

[3] Following the death of his father, Langton went missing and was discovered in New York City, where he was en route to see his brother Donald in Canada.

Following Seagulls Over Sorrento, he acted in many plays, including Agatha Christie's Rule of Three and The Devil's Disciple, where he met and formed a friendship with Tyrone Power.

David Langton had started his television career in the 1950s and went on in the 1960s to appear in The Troubleshooters, Out of the Unknown, The Avengers, The Champions, Dr. Finlay's Casebook and Special Branch.

Langton achieved international notice for playing husband and father Richard Bellamy in the period drama Upstairs, Downstairs which began in 1971.

Following the success of Upstairs, Downstairs, Langton appeared in the 1972 BBC Television adaptation of Dorothy L. Sayers's Lord Peter Wimsey mystery Clouds of Witness, as the Duke of Denver (older brother to Lord Peter Wimsey); the film The Incredible Sarah (1976); and Robert Altman's science fiction film Quintet (1979), starring Paul Newman.

He played Victor Frankham in Hammer House of Mystery and Suspense (1984), and appeared in the film The Whistle Blower (1986) opposite Michael Caine.