McGillion returned to Scotland with his family during his early teens, for a few years, while his father worked on the Shetland oil rigs.

In 2004, McGillion was cast in the science fiction series Stargate Atlantis as the Scottish medical doctor, Carson Beckett.

McGillion has appeared in films, The Traveler with Val Kilmer, Confined with Emma Caulfield, and The Deal with Christian Slater.

McGillion expressed great interest in auditioning for the role of Montgomery Scott in the 2009 eleventh Star Trek film.

[4] McGillion appeared in season 7 on the TV series 24 as Dr. Levinson, a doctor who tried to extract a dangerous pathogen from Jack Bauer's bloodstream.