Garreth graduated from Memorial University of Newfoundland with Bachelor of Arts Honours in German and History in 2013 and the University of New Brunswick with a Juris Doctor in 2017. In 2017 he was awarded ninth place oralist in the Canadian National Round of the Philip C Jessup International Law Moot Court Competition, the oldest and largest moot competition in the world. After returning to Newfoundland and Labrador he articled under Richard Rogers, QC and has remained with Rogers Rogers Moyse. Since being called, Garreth has focused on personal injury, corporate law, and immigration matters.
Garreth is currently a committee member with Sandbox Gaming, a local charity organization that raises money for programs that promote play and social interaction among children across the province.