Born in Walshaw, near Bury, Lancashire, England,[4] the son of Allan and Gladys Mabel (née Curson),[5] Smethurst was raised in Sheringham, Norfolk. His mother came from the nearby village of Stiffkey. He later became a postman in Grimsby.[

Smethurst hummed tunes on his daily post round for twelve years, writing and singing songs in his native Norfolk dialect.[4] An audition tape sent to a BBC regional radio programme earned him a spot on Ralph Tuck's East Anglian VHF radio show Wednesday Morning, and Tuck recorded Smethurst on his own record label, The Smallest Recording Organisation in the World, based in Lowestoft. A four track EP made the EP charts in 1965 and, after another EP release by Ralph Tuck, and an album The Singing Postman's Year, he was signed to EMI who re-released earlier songs and recorded new items. He made numerous live and promotional performances, including on Top of the Pops, but was afflicted by nerves and stage fright.

In 1966, the Singing Postman's best known hit "Hev Yew Gotta Loight, Boy?" won Smethurst the Ivor Novello Award for best novelty song of the year. Rolf Harris recorded a cover version without success. The song had a small comeback in 1994, when it was featured on a television commercial for Ovaltine.

Smethurst left the music industry in 1970, later admitting he had an alcohol problem and that he had spent all of his money and was penniless. He spent his last few years living quietly in a Salvation Army hostel in Grimsby, where he died from a heart attack in December 2000.

In September 2010, a BBC Radio 4 programme, "In Search of the Singing Postman", was broadcast which was written and presented by D. J. Tayl