Doonican was the youngest of eight children. His father died when he was a teenager, so it was necessary for him to leave De La Salle College, Waterford and get jobs in factories fabricating steel and making orange boxes.

He was from a musical family and started performing in his home town and in a summer season at Courtown Harbour. He was then featured on Irish Radio and appeared in the first ever television broadcast from Waterford. He then joined a band which toured Ireland playing the drums. In 1951 he moved to England to join another group, The Four Ramblers, who toured and performed on BBC Radio shows broadcast from factories.

He eventually went solo and had a radio show as well as performing concerts and cabaret. In 1963 he was booked to appear on Sunday Night at the London Palladium. As a result of this performance, he was offered his own show on BBC television, lasting for over twenty years and moving to Saturday as its popularity grew.

It featured his relaxed crooner style performance sitting in a rocking chair, as well as a number of comic Irish songs, notably "Paddy McGinty's Goat", "Delaney's Donkey", and "O'Rafferty's Motor Car", on which he accompanied himself on acoustic guitar.

He often wore cardigans, which together with the rocking chairs he often sat in became his trade mark, and was sometimes compared to American singer Perry Como though Doonican has claimed his main influence was Bing Crosby. As a variety show, there were a number of other acts featured and performers such as Dave Allen had early exposure on the show.

The Palladium performance also kick-started his recording career. Between 1964 and 1973 he was rarely out of the UK Singles Chart, his greatest successes including the singles "Walk Tall", "The Special Years", "What Would I Be", "If The Whole World Stopped Loving", and "Morning"; and the albums 13 Lucky Shades of Val Doonican, and Val Doonican Rocks, But Gently. He also sang the theme song to the film Ring of Bright Water.