Raised in the Oatlands neighbourhood of southern Glasgow,[1] Dornan joined the Scottish National Party in 1996[2] and previously worked for Stewart Maxwell (MSP).

[11] Later in July 2020, the SNP National Executive Committee voted have an all-woman shortlist for the Glasgow Cathcart Scottish Parliamentary constituency, ending his bid of standing for the seat again.

Dornan was selected to stand for the SNP in the Glasgow Cathcart Scottish Parliamentary constituency and held the seat with 57% of the vote.

[16][17] In July 2021 Dornan was reported to the Ethical Standards Commissioner after commenting on a post by Conservative cabinet minister, Jacob Rees-Mogg.

Conservative MSP Russell Findlay, a former crime reporter who had acid thrown at his face by a gangster, accused Dornan of “gaslighting” Smith and warned, “Cowardly attacks on journalists by the lunatic brigade in Scotland have become increasingly toxic since 2014.

"[23] Dornan has made a series of comments criticising Operation Branchform, the Police Scotland investigation into alleged fundraising fraud in the SNP.

[24] In 2024, after Chief Constable of Police Scotland Jo Farrell confirmed that Operation Branchform was still ongoing and was unable to offer an end date to the investigation, Dornan shared the post on Twitter and wrote: "I have May 2026 in the draw."

Dornan further denounced the investigation as a "farce" in conversation with other Twitter users: "The minute we're seen to even attempt to interfere in police business we would, rightly, be slaughtered.