Secombe was born in a council house in the St Thomas district of Swansea, the third of four children of Nellie Jane Gladys (née Davies), a shop manageress, and Frederick Ernest Secombe, a grocer. From the age of 11 he attended Dynevor School, a state secondary school in central Swansea.

His family were regular church-goers, belonging to the congregation of St Stephen's Church in Danygraig. A member of the choir, Secombe would - from the age of 12 - perform a sketch entitled The Welsh Courtship at church socials, acting as "feed" to his sister Carol. His elder brother, Fred Secombe was the author of several books about his experiences as an Anglican priest and rector.

After leaving school in 1937, Secombe became a pay clerk at Baldwin's store. In 1938 he joined the Territorial Army, serving as a Lance Bombardier in the Royal Artillery. He would refer to the unit in which served during World War II in the North African Campaign, Sicily, and Italy as "The Five-Mile Snipers".

He first met Spike Milligan in Tunisia. Milligan's artillery battery had a larger calibre artillery piece that was too big for the gun pits that Secombe's unit's cannon had used. The rest of Secombe's battery had already moved and he was with the last elements in some tents at the foot of a cliff below their former position. The officers in Milligan's battery had not bothered to enlarge the pits. When Spike's cannon fired its first shell, the recoil drove the gun up out of the pit and over the cliff. Secombe recalled that when the weapon fell outside the tent, he and his mates thought, "My God! They're throwing cannons at us!" A moment later, the flap of his tent opened and Spike poked his head in and said in his Eccles' voice, "Has anyone seen a gun?" Secombe replied "What colour?".

When Secombe visited the Falklands to entertain the troops after the 1982 war in the islands, his old regiment promoted him to the rank of sergeant — 37 years after he had been demobbed.

Secombe joined the cast of the Windmill Theatre in 1946, using a routine he had made up in Italy about how people shaved. Secombe always claimed that his ability to sing could always be counted to save him when he bombed. Both Milligan and Sellers credited him with keeping the act on the bill when club owners had wanted to sack them.

After a regional touring career, his first break came in radio when he was chosen as resident comedian for the Welsh series Welsh Rarebit, followed by appearances on Variety Bandbox and a regular role in Educating Archie.

Secombe met Michael Bentine at the Windmill Theatre, and was introduced to Peter Sellers by his agent Jimmy Grafton. Together with Spike Milligan, the four wrote a comedy radio script entitled Crazy People. Produced by the BBC's Peter Ross, this was eventually to turn into The Goon Show. First broadcast on 28 May 1951, the show remained on the air until 1960. Secombe was notable for playing Neddie Seagoon, the focus of many of the show's absurd plots.

While the success of The Goon Show meant that he needed to do no other work, Secombe continued to develop a dual career as both a comedy actor and a singer. At the beginning of his career as an entertainer, his act would end with a joke version of the duet Sweethearts, in which he sang both the baritone and falsetto parts. Trained under Italian maestro Manlio di Veroli, he emerged as one of the few bel canto tenors, and had a long list of best-selling record albums to his credit.

In 1958 he appeared in the film Jet Storm, which starred Dame Sybil Thorndike and Sir Richard Attenborough in the title role of Davy - the last feature film made at Ealing Studios.

The power of his voice allowed Secombe to appear in many stage musicals. This included 1963's Pickwick, based on Dickens's The Pickwick Papers, which gave him the number eighteen hit single "If I Ruled the World" - his later signature tune. In 1965 the show was produced on tour in the United States, where on Broadway he garnered a nomination for a Tony Award for Best Actor in a Musical. He also appeared in 1967's The Four Musketeers, Mr. Bumble in Carol Reed's 1968 film of Lionel Bart's Oliver!, and in the Envy segment of The Magnificent Seven Deadly Sins.

He would go on to star in his own show, The Harry Secombe Show, which debuted on Christmas Day 1968 on BBC One and ran for thirty one episodes until 1973. A sketch comedy show featuring Julian Orchard as Secombe's regular sidekick, the series also featured guest appearances by fellow Goon Spike Milligan as well as leading performers of the time such as Ronnie Barker and Arthur Lowe. Secombe would go on to star in similar vehicles such as Sing a Song of Secombe and ITV's Secombe with Music during the 1970s.

Later in life, Secombe (whose brother Fred Secombe was a priest in the Church in Wales, part of the Anglican Communion) attracted new audiences as a presenter of religious programmes, such as the BBC's Songs of Praise and ITV's Highway. He was also a special programming consultant to Harlech Television.

He was knighted in 1981, and jokingly referred to himself as Sir Cumference (in recognition of his rotund figure). In 1990, he was one of the few celebrities to be honoured by a second appearance on This Is Your Life, having had a first program produced in 1958.

Secombe suffered a stroke in 1997, from which he made a slow recovery, he was then diagnosed with prostate cancer in September 1998. After suffering a second stroke in 1999, he was forced to abandon his television career, but made a documentary about his condition in the hope of giving encouragement to other sufferers. Secombe had diabetes in the latter part of his life.

Harry Donald Secombe died April 11, 2001 at the age of 79, from prostate cancer, in hospital in Guildford, Surrey. His ashes are interred at the parish church of Shamley Green, and a later memorial service to celebrate his life was held at Westminster Abbey on 26 October 2001. As well as family members and friends, the service was also attended by Charles, Prince of Wales and representatives of Prince Philip, Duke of Edinburgh, Anne, Princess Royal, Princess Margaret, Countess of Snowdon and Prince Edward, Duke of Kent. On his tombstone is the inscription: "To know him was to love him."

The Secombe Theatre at Sutton, London bears his name in memory of this former local personality.

Secombe met Myra Atherton at the Mumbles dance hall. The couple were married from 1948 until his death, and had four children:

• Jennifer Secombe, married to actor Alex Giannini. She was also her father's agent.
• Andy Secombe, a voice and film actor, and an author
• David Secombe, a writer and photographer
• Katy Secombe, an actress

Singles

• "On with the Motley" (1955) UK #16
• "Bless This House" (1960) UK
• "If I Ruled the World" (1963) UK #18
• "This Is My Song" (1967) UK #2

Albums

• Sacred Songs (1962) UK #16
• Secombe's Personal Choice (1967) UK #6
• If I Ruled the World (1971) UK #17
• Bless This House: 20 Songs Of Joy (1978) UK #8
• Captain Beaky and His Band

Books

• Alternative ISBNs for 2004 publication: ISBN 978-1-86105-811-9; ISBN 1-861-05811-X (paperback).
• The Goon Omnibus (Goon For Lunch). London: The Companion Book Club (1978)
• Twice Brightly London: The Companion Book Club