[3][4] He returned to Scotland in 1988 at the age of 18 to study at the University of Glasgow, where he achieved an MA Honours Degree in theatre, film and television.
[6] Hemphill said that despite living in Canada, he "always felt Scottish", claiming that "My dad was from Maryhill, my mum was from St George’s Cross, and it seemed that everyone on the West Island of Montreal was from somewhere else".
In 1990, he performed at the Edinburgh Fringe with Rab Christie and Neil Warhurst as the "Trio Brothers Troup", where they won the 1990 "So You Think You're Funny" trophy.
However, his best known performances are alongside Ford Kiernan in the television sketch show Chewin' the Fat and its spin off, Still Game.
In series three of Still Game, Hemphill's brother Steve has a cameo as a CN Tower lift operative.
The series ended following the sixth series in 2007, with Ford Kiernan, Greg Hemphill and Paul Riley's company Effingee Productions which produced Still Game, thought to have split up after Riley walked away to go it alone after being refused more control over the future of the company by Kiernan.
[15] On 24 October 2013 Kiernan confirmed in the Daily Record that Kenny Boyle's tour of the original stage show had been one of the instigating factors for Still Game's return.
[33] Hemphill has been involved in the Scottish wrestling scene, matched against actor, comedian and writer, Robert Florence.
[34][35] Hemphill guest-starred in an episode of the award-winning children's television programme Katie Morag in 2014, playing the part of Donald John Cameron.
[36] Hemphill starred as Mr Sawdust in two series of the CBeebies television show Olga da Polga alongside his wife Julie Wilson Nimmo.
[38] In March 2023, Hemphill featured on a BBC Scotland programme as part of the broadcaster's centenary celebrations, alongside wife Julie Wilson Nimmo and Still Game co-star Sanjeev Kohli.
[41] In 2016, alongside Donald McLeary, Hemphill wrote the script for the horror/comedy film West Skerra Light.
[44] In 2017, alongside Hopscotch Films, Hemphill was involved in directing the black comedy ghost-hunting drama Long Night at Blackstone.