Williamson's mother played the piano. At school he learned to play the recorder by ear, pretending to read music. The teacher found out and banned him from music lessons. He went to Wester Elchies School, then Aberlour House and Gordonstoun in Moray. He taught seamanship and navigation at Burghead before going to Edinburgh College of Art. It was there in 1955 that he met Ronnie Browne, with whom he would team up in The Corries. The partnership lasted over thirty years.
In 1955 Williamson met Ronnie Browne at Edinburgh College of Art. This meeting started a 35 year long partnership.
Williamson joined Bill Smith and Ron Cockburn to form the "Corrie Folk Trio" in 1962. A corrie is a circular dip in a highland mountain. They chose it to evoke the Scottish landscape.
The trio's first performance was in the Waverley Bar in St Mary's Street, Edinburgh. After a few weeks Cockburn left. They had already accepted an engagement at the Edinburgh Festival so Williamson suggested that Ronnie Browne should be brought in to make up numbers. They also added female Irish singer Paddie Bell to become the "Corrie Folk Trio and Paddie Bell". The audience was only eight people for the debut of this line-up but by the end of the festival it was house full at every performance.
By 1965, Paddie Bell and Bill Smith left. Williamson was a talented multi-instrumentalist and Browne was the singer. They cancelled all engagements for a few months to practise intensively. Under the new name, "The Corries", they performed at the Jubilee Arms Hotel in Cortachy, Angus. The response encouraged them to continue as a duo.
Williamson was a skilled woodworker. In the summer of 1969 he invented the 'combolins', two complementary instruments which combined several into a single instrument. One combined a mandolin and a guitar (along with four bass strings operated with slides) , the other combined guitar and the 12-string Spanish bandurria, the latter being an instrument Williamson had played since the early days of the Corrie Folk Trio.
Originally conceived as a way to combine several of the many instruments they carried around on tour - the Corries' long row of chairs behind them on stage bearing instruments is legendary - the combolins in fact became an additional two instruments for the tour van. Most often, Browne played the guitar/mandolin instrument with bass strings, and Williamson the other, which also had 13 sympathetic strings designed to resonate like the Indian sitar.
The wood for the instruments was obtained from antique hardwood furniture as well as premium grade Tyrolean spruce, and featured Williamson's artistic embellishments in silver and mother of pearl. The Corries' next album. Strings and Things (1970) was specifically designed to showcase the new instruments and featured detailed descriptions of them on the rear sleeve.
As a young man, Roy Williamson played rugby for Edinburgh Wanderers. However, he suffered from asthma and before a series of concerts he would deliberately cease treatment in order to provoke attacks and gain temporary immunity. He continued performing till 1989. He died of a brain tumour in 1990.