Hird was born in the Lancashire seaside town of Morecambe. She first appeared on stage at the age of two months in a play her father was managing. She worked at the local Co-op before joining the Morecambe Repertory Theatre. Her family background was largely theatrical: her mother, Marie Mayor, had been an actress, while her father managed a number of entertainment venues in Morecambe, including the Royalty Theatre where she made her first appearance, and the Central Pier. Thora often described her father, who initially did not want her to be an actress, as her sternest critic and attributed much of her talent as an actress and comedienne to his guidance. Although Hird left Morecambe in the late 1940s, she retained her affection for the town, referring to herself as a “sand grown’un”, the colloquial term for anyone born in Morecambe. Initially she made regular appearances in films, including the wartime propaganda film Went the Day Well? (1942, known as 48 Hours in the USA), in which she is shown wielding a rifle to defend a house from German paratroopers. She worked with the British film comedian Will Hay, and featured in The Entertainer (1960), which starred Laurence Olivier, and in A Kind of Loving (1962), with Alan Bates.

Thora Hird gained her highest profile in television comedy, notably the sitcoms Meet the Wife (1963–66), In Loving Memory (1979–86), Hallelujah! (1981-1984), and for nearly two decades in Last of the Summer Wine (1986–2003). However, she played a variety of roles, including the nurse in Romeo and Juliet, and won BAFTA Best Actress awards for her roles in two of Alan Bennett’s Talking Heads monologues. She starred as Captain Emily Ridley in the sitcom Hallelujah! (1981–84) about the Salvation Army, a movement for which she had a soft spot throughout her life. Hird also portrayed Mrs Speck, the housekeeper of the Mayor of Gloucester in The Tailor of Gloucester (1989). She played the screen mother of Deric Longden in Wide Eyed and Legless (aka the Wedding Gift) and Lost for Words which won her a BAFTA for Best Actress. Hird was a committed Christian, hosting the religious programme Praise Be!, a spin-off from Songs of Praise on the BBC. Her work for charity and on television in spite of old age and ill health made her an institution. Her advertisements for Churchill stairlifts also maintained her in the public eye. She was created an Officer of the Order of the British Empire (OBE) in 1983, and raised to Dame Commander (DBE) in 1993. She received an honorary D.Litt. from Lancaster University in 1989. In December 1998, already using a wheelchair, Dame Thora played a brief but energetic cameo role as the mother of Dolly on Dinnerladies, a sarcastic character, who was particularly bitter towards her daughter. Her last work was for BBC Radio 7: a final monologue written for her by Alan Bennett entitled The Last of the Sun, in which she played a forthright, broad-minded woman, immobile in an old people’s home but still able to take a stand against the censorious and politically correct attitudes of her own daughter. She was the subject of This Is Your Life on two occasions: in January 1964 when she was surprised by Eamonn Andrews, and in December 1996, when Michael Aspel surprised her while filming on location for Last of the Summer Wine.

Hird died on 15 March 2003 aged 91 at Brinsworth House, Twickenham, London, after suffering a stroke. A memorial service was held on 15 September 2003 at Westminster Abbey attended by over 2,000 people, including Alan Bennett, Sir David Frost, Melvyn Bragg and Victoria Wood. Hird married James Scott in 1937. They had a daughter, actress Janette Scott, in 1938. Hird was widowed in 1994.