[5] As a loosehead prop, McKellar played more than 150 premier grade games over a decade at Souths Rugby Club in Brisbane, winning a premiership in 2000.
[6] McKellar began learning the art of coaching at Wicklow, a small rugby club just outside Dublin in Ireland.
[6] In February 2013, McKellar moved to Japan to take up a position as forwards coach of Top League team NTT DoCoMo Red Hurricanes.
[6] After the launch of the National Rugby Championship, he was appointed as head coach of the University of Canberra Vikings team to play in the new competition.
[11] In August 2021 it was announced McKellar would wind up a successful five-year stint as Brumbies head coach at the end of the 2022 Super Rugby season and would remain in his position with the Australia national team.