Grigg made his 6 Nations debut in 2018, coming on as a replacement for Pete Horne in the 72nd minute in Scotland's historic Calcutta Cup victory at BT Murrayfield. He featured in the side's next game against Ireland, again coming on for Horne in the final 10 minutes, before he was awarded his first 6 Nations start in Scotland's final championship test in Rome to secure 3rd place in the 2018 NatWest 6 Nations.

Grigg signed for current team Glasgow Warriors at the start of the 2015/16 season. A hard-running centre, he first caught the eye when playing in New Zealand in 2011 for Petone. Having played for the Hurricanes Development XV, Grigg moved to Scotland, and has impressed in club rugby for Stirling County and progressing through the BT Sport Scottish Rugby Academy.

Grigg also represented Scotland 7s in the World Rugby Seven Series in Wellington in 2015.