By the late 1950s, Sullivan was working at the His Master's Voice record label as assistant to producer Wally Ridley.
[2][3] Although the details of their first contact are disputed, Sullivan was also one of the first to recognise the recording potential of Welsh singer Tom Jones, then known as Tommy Scott.
In late 1964, Sullivan produced Tom Jones' single, "It's Not Unusual", insisting that a brass section be used in the arrangement.
[4][5] The song became a number one hit on the UK Singles Chart in March 1965, launching Jones' career.
He also produced the UK number one hit by Engelbert Humperdinck, "The Last Waltz", and records by Solomon King, Jim Capaldi, and Demis Roussos, among others.