Billy Connolly was born in Glasgow, Scotland to Mary and William Connolly, the son of an Irish immigrant.

Connolly was brought up in the Anderston and later, Partick districts of Glasgow and attended St. Gerard's Secondary School.

He started his working life as a welder in a Glasgow shipyard but left that trade to become a folk singer. Together with Tam Harvey he started a group called the Humblebums, which later included Gerry Rafferty. Connolly sang, played banjo and guitar and entertained the audience with his humorous introductions to the songs. Eventually the duo broke up and Billy went solo. His first solo album in 1972, Billy Connolly Live! on Transatlantic Records, features Billy as a singer, songwriter and musician.

His early albums were a mixture of comedy performances with musical interludes. Among his best known musical performances were "The Welly Boot Song", a comical ode to the working class which became his theme song for several years; "In the Brownies", a parody of the Village People classics "Y.M.C.A." and "In the Navy" (for which Connolly filmed a music video); "Two Little Boys in Blue", a tongue-in-cheek indictment of police brutality done to the tune of Rolf Harris' "Two Little Boys"; and the ballad "I Wish I Was in Glasgow" which Connolly would later perform on a guest appearance on the 1990s American sitcom, Pearl. By the late 1980s, Connolly had all but dropped the music from his act, though he still records the occasional musical performance. Most recently, he sang a song during the film Lemony Snicket's A Series of Unfortunate Events.

It is as a stand-up comedian that Connolly is best known. His observational humour is idiosyncratic. He talks about himself, who he is, where he's been, what he thinks and how he reacts to the world around him. He has outraged audiences, critics and, of course the media, with his free use of the word fuck. He has used masturbation, blasphemy, defecation, flatulence, sex, his father's illness and his aunts' cruelty to entertain. By exploring these subjects with humour, Connolly has done much to strip away the taboos surrounding them. Yet he does not tell jokes in the conventional way. At the end of a concert the audience can be convulsed with laughter but few can remember a specific "funny" line.

One of Connolly's most famous comedy skits is "The Crucifixion", an early 1970s recording in which he likens Christ's Last Supper to a drunken night out in Glasgow. The recording was banned by many radio stations at the time.