Robertson became a full-time author in the early 1990s. From 1993 to 1995 he was the first writer in residence at Hugh MacDiarmid's house outside Biggar, Lanarkshire. Robertson had already been heavily influenced by MacDiarmid and MacDiarmid's Scots language poetry prior to this appointment. His early short stories and first novel used contemporary and historical life in Edinburgh as a key theme, drawing on his experience of living there intermittently during his PhD and during the later 1990s before moving to Fife, and subsequently Angus. Each of his three novels has been influenced to a degree by where he was living when he wrote them. "Joseph Knight" is based on the true story of a slave brought from the Caribbean to Scotland, and the novel revolves primarily around the cities of Dundee, near where Robertson was then living, and Edinburgh. "The Testament of Gideon Mack", meanwhile, is set in a fictitious rural village that resembles the villages of eastern Scotland bordering the Highlands between Dundee and Aberdeen where Robertson currently lives. His novels, therefore, feature the Scottish urban and rural landscape as prevalently as Scottish history between the 17th and 20th centuries.