His uncle George Dempster of Dunnichen sent him to Rome to study art.
[3][4] Willison went to India and painted portraits, including those of some Indian princes and their families.
[3][4] In 1756 Willison was awarded a prize for a drawing of flowers by the Edinburgh Society for the Encouragement of the Arts and Sciences, and in the two following years his name again figured in the prize-list.
There he produced a series of portraits that were destined for the British political supporters of the Nawab.
[4] A number of Willison's portraits were engraved by Valentine Green and James Watson.