In their review of the series, the British Theatre Guide said "Sir Donald's gorgeous plummy tones are a joy to listen to whatever he is saying but when he is extolling the virtues of one of his own favourite theatres, the pleasure is heightened. At his first entrance, he announces that he is "tingling with excitement" which is just what one wants from a tour guide. Soon enough, so are viewers."
Sinden was colour blind and suffered from asthma, which prevented him from joining the armed forces during the Second World War and suffered from negative buoyancy, meaning that he was unable to float or swim in water, which was discovered while filming The Cruel Sea when the ship was sinking. Co-star Jack Hawkins saved him from drowning in the open-air water-tank at Denham Studios.
In 1949, he appeared in The Heiress at the Theatre Royal, Haymarket opposite Ralph Richardson and Peggy Ashcroft, directed by John Gielgud. In his Sky Arts documentary series Great West End Theatres, Sinden said that the play ran for 644 performances (19 months) and he was the only member of the cast not to have missed a performance: "As the play is the longest run in the [Haymarket] theatre's history, I therefore gave more consecutive performances in this theatre than any other actor since it was built in 1820." The management gave him an engraved silver ashtray as a present in recognition of the fact, which he showed in the episode.
Sinden was born in St Budeaux, Plymouth, Devon on 9 October 1923. The middle child of Alfred Edward Sinden and his wife Mabel Agnes (née Fuller), he had an elder sister Joy who was an English teacher at Claverham Community College in Battle, East Sussex, and a younger brother Leon (1927–2015), likewise an actor. They grew up in Ditchling, where their home 'The Limes' doubled as the local chemist's shop.
Sinden received, posthumously, the Gielgud Award for Excellence in the Dramatic Arts at the Guildhall, London during the 2014 Theatre Awards UK ceremony, held on 19 October. The award was collected on his behalf by his son Marc Sinden.
Sinden became associated with his character of "Benskin" in the Doctor film series as the duffel-coated medical student, regularly failing his finals and spending most of his time chasing pretty nurses, accompanied by his trade-mark "wolf-growl".
The Daily Telegraph's review states "Great West End Theatres is a lovely documentary series, made by the director Marc Sinden. Its star, and – it transpires – the best documentary frontman of all time, is his actor-father: Sir Donald Sinden, 90 years old next month. Sir Donald has been let loose and the effect is enchanting beyond belief. It is also, at times, incredibly funny. One has the sense of a lifetime spent in this world, being poured out for our delight like glasses of vintage champagne."
Sinden's distinctive voice was heard frequently on radio, including as Sir Charles Baskerville in a BBC Radio 4 adaptation of the Sherlock Holmes story The Hound of the Baskervilles. He starred in multiple adaptations of John Dickson Carr's Dr. Gideon Fell mysteries, including The House on Gallows Lane, The Hollow Man and Black Spectacles, To Wake the Dead, The Blind Barber and The Mad Hatter Mystery.
For the 1976 Stratford season and then at the Aldwych Theatre in 1977, Sinden won the Evening Standard Award as Best Actor for his performance in the title role of King Lear (with Michael Williams as the Fool). Meanwhile, he was also portraying in repertory, Benedick (regarded as "the most admired Benedick in living memory") opposite Judi Dench's Beatrice in John Barton's highly acclaimed 'British Raj' revival of Much Ado About Nothing, and in the same time frame also rehearsing the third season of the LWT sitcom Two's Company with Elaine Stritch during the daytime and filming the show at the studio in front of a live audience on Sunday evenings. He claimed "RSC money isn't very good compared with a normal commercial theatre rate. I was on their 'star' salary, which meant it worked out at about £47 per performance! You work for them 'for the honour' of doing the greatest classical plays, not for the money, so you have to make up the financial short-fall somewhere".
Sinden wrote two autobiographical volumes: A Touch of the Memoirs (1982) and Laughter in the Second Act (1985), edited the Everyman Book of Theatrical Anecdotes (1987), wrote a book to coincide with his BBC TV series The English Country Church (1988) and a collection of "epitaphs and final utterances" titled The Last Word (1994).
He was the subject of an extended edition of This Is Your Life in 1985 when he was surprised by Eamonn Andrews. He also appeared on Lily Savage's Blankety Blank.