Hurndall was born in Darlington. After training at the Royal Academy of Dramatic Arts, he appeared in several plays at Stratford-upon-Avon. Hurndall acted with the BBC radio drama repertory company from 1949 to 1952.
In 1958 he became the third host of the Radio Luxembourg program This I Believe, which had originally been hosted by Edward R. Murrow on the U.S. CBS Radio Network from 1951 to 1955. It was edited in London for rebroadcast on Radio Luxembourg's 208 wavelength with a British style of presentation.
Hurndall appeared in many radio and stage plays, films and television series over the course of his lengthy career, including The Avengers, The Persuaders!, Whodunnit! (with another Doctor, Jon Pertwee), and Bergerac. He played the suave London gangster Mackelson in the 1968 drama series Spindoe and did a camp turn as a gay antique dealer who takes a shine to Harold Steptoe in the comedy Steptoe and Son.
In 1983, to celebrate the twentieth anniversary of the long-running BBC science fiction television series Doctor Who, producer John Nathan-Turner planned a special event, The Five Doctors, a ninety-minute episode to feature the five actors who had at that point played the role of the Doctor. However, William Hartnell, the actor who originated the role, had died in 1975. The show's unofficial fan consultant, Ian Levine, had seen Hurndall in Blake's 7, another BBC science fiction series, and suggested him to the producers as a possible replacement. Hurndall eventually won the role of the First Doctor, playing him as acerbic and temperamental but in some ways wiser than his successors. When the Fourth Doctor, Tom Baker, decided not to appear in the programme, Hurndall's role was beefed up slightly to have the First Doctor take a greater part in the action.
Hurndall died of a heart attack, less than half a year after the first broadcast of The Five Doctors. As with William Hartnell a decade earlier, Hurndall's heart condition was known at the time of filming the show; those involved with the production of The Five Doctors subsequently praised Hurndall's bravery in accepting such a demanding part and shoot. A myth claims that he was going to reprise his role in The Two Doctors prior to his death, but knowledge of his heart condition makes this more than likely a false rumour.
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