The midfielder has since gone on to become a fixture under both Gregor Townsend and Dave Rennie, making 66 appearances to date in a Glasgow jersey.
Renowned for hard running, the most recent of Grigg's 16 tries for the club came in November's clash with Exeter Chiefs at Sandy Park.
His defensive prowess also came to the fore in this season's Heineken Champions Cup; Grigg's tally of 16 tackles in the home triumph over Sale Sharks was more than any other back in the competition, helping his side to a 13-7 victory at Scotstoun.
Grigg has earned nine Scotland caps to date, making his debut in the 2018 Calcutta Cup clash at BT Murrayfield before going on to play his part in 2019's 38-38 draw with the Auld Enemy at Twickenham.
"It was an easy enough decision to stay," Grigg told glasgowwarriors.org.
"I spoke to Danny (Wilson) a wee while ago and he said he was keen for me to stay, which is exactly what you want to hear from your incoming head coach. I told him I was keen to stay as well, and that was that.
"Glasgow's like a second home to me now. The boys are really good to me and it's a special environment around the club on a day-to-day basis.
"Four years ago I was playing for Stirling County, and now to have over 60 caps for the Warriors has been an amazing journey so far. I just want to play as well as I can for this club, starting with Friday night if I'm selected."
Glasgow Warriors assistant coach, Kenny Murray said: "We're extremely pleased that Nick has re-signed with the club.
"He contributes significantly to our game plan in both attack and defence and has grown into an important player for us over the last four years.
"Nick is a great presence to have in and around the club on a daily basis, and we're excited to continue to work with him over the next couple of seasons."
Incoming Head Coach, Danny Wilson added: "Nick is a powerful ball carrier and an aggressive defender.
"He has contributed a lot to the club over the last four years and we're delighted he's going to continue his career in Glasgow."