Kenneth Williams was born in King's Cross, London; his father, Charlie, was a railway van boy, but later managed a hairdresser's shop in Marchmont Street. At the age of 14 in 1940, Kenneth Williams was sent to the School of Lithography off Fleet Street. He was soon evacuated, with the start of the War, to Bicester in Oxfordshire. He returned to London to resume his lithography studies in 1941. In 1943 Kenneth Williams was briefly with an amateur dramatics troupe, the Tavistock Players.

In February 1944 he was inducted into the armed forces with a period with the Border Regiment in Cumbria to improve his fitness. He was then posted to the Survey Section of the Royal Engineers. In April 1945 he was sent to Bombay via a troop ship from Greenock. In August 1945 he was sent to a map reproduction unit in Ceylon (now Sri Lanka).

He soon obtained a transfer to Combined Services Entertainments. Williams failed his first audition but his drawing skills were used for posters and gave him the opportunity to try again. He played the part as the detective in Seven Keys to Baldpate at the Victoria Theatre, Singapore, and he secured his place in the troupe.

Kenneth Williams returned to London in December 1947 and took parts in a number of plays before starting to obtain parts in various BBC radio programmes. This led to parts in films and television programmes. He became friendly with Joe Orton and Kenneth Halliwell, and went on holiday with them to Morocco in 1965. Kenneth Williams also played Inspector Truscott in Joe Orton's play Loot in 1965.

Kenneth Williams became most well known for his roles in the Carry On films. The pool of actors who also played roles in this series of 30 films included the gay men Charles Hawtrey and Frankie Howerd. He died in London taking an overdose of barbiturates; his father had also killed himself.

Throughout his life he kept a diary (published only after his death), where he wrote:

Determined to hide it and not give a sign
Of the desperate ego and id that is mine.
Never to speak of my love for a man.
Hope that God loves me, for no one else can

Films: Trent's Last Case (1952) The Beggar's Opera (1952) The Seekers (1954) Moby Dick (1956) Carry on Sergeant (1958) Carry on Nurse (1959) Carry on Teacher (1959) Carry on Constable (1960) Make Mine Mink (1960) Carry on Regardless (1961) His and Hers (1961) Carry on Cruising (1962) Carry on Jack (1963) Carry on Cleo (1964) Carry on Spying (1964) Carry on Cowboy (1965) Carry on... Don't Loose Your Head (1966) Carry on Screaming (1966) Carry on Doctor (1967) Carry on... Follow That Camel (1967) Carry on... Up the Khyber (1968) Carry on Again Doctor (1969) Carry on Camping (1969) Carry on Loving (1970) Carry on at Your Convenience (1971) Carry on Henry (1971) Carry on Abroad (1972) Carry on Matron (1972) Carry on Dick (1974) Carry on Behind (1975) Carry on Emmanuele (1978) That's Carry on (1978) The Hound of the Baskervilles (1978)

Theatre: Peter Pan (1952) Share My Lettuce (1957) Pieces of Eight (1959) One Over the Eight (1961) Loot (1965) TV: The Wonderful Visit (1952) Misalliance (1954) Cold Comfort Farm (1956) The Man Who Could Work Miracles (1956) Catch as Catch Can (1964) Books: Acid Drops (1980) Back Drops: Pages From a Private Diary (1983) Just Williams: An Autobiography (1985) The Kenneth Williams Diaries (1993) The Kenneth Williams Letters (1994) The Complete Acid Drops (1999)