Raised in the Collyhurst district of Manchester, Dawson began his entertainment career as a club pianist ("I finally heard some applause from a bald man and said 'thank you for clapping me' and he said 'I'm not clapping - I'm slapping me head to keep awake.'"); but found that he got more laughs by playing wrong notes and complaining to the audience. He made his television debut in the talent show, Opportunity Knocks, and was seldom absent from British television screens in the years that followed. His best known routines featured Roy Barraclough and Dawson as two elderly women, Cissie Braithwaite and Ada Sidebottom who, having worked in a mill in their youth, spoke some words aloud and mouthed others--particularly those pertaining to bodily functions and sex; they also repeatedly pushed up their bosoms, in pantomime dame style, an act copied faithfully from his hero, Norman Evans. Dawson's humour, though earthy, was seldom coarse, and he was as popular with female as with male audiences.

Before his fame Dawson wrote poetry - a guilty secret for someone of his earthy background - and he harboured literary ambitions throughout his career. He wrote many novels but was always regarded solely as an entertainer in the public imagination, and this saddened him.

Having broken his jaw in a boxing match, Dawson was able to pull grotesque faces by pulling his jaw over his upper lip.

Television series in which he appeared included Sez Les, The Les Dawson Show, Dawson's Weekly, and the quiz show Blankety Blank, which he presented for some years. He died from a heart attack while waiting for treatment in a hospital in Whalley Range, Manchester. He lived for many years in Lytham St Annes, near Blackpool.

In a 2005 poll to find The Comedian's Comedian, he was voted amongst the top 50 comedy acts ever by fellow comedians and comedy insiders.