The 23-year-old follows Jack Oliver in signing professional terms with Franco Smith’s squad, as preparations continue ahead of the new campaign.
Formerly part of the Bristol Bears academy system, the Clevedon RFC product was initially invited to train with the Warriors after impressing for Stirling Wolves in the FOSROC Super Series, before joining the Glasgow Warriors academy ahead of the 2024/25 campaign.
Duncan has made 11 appearances to date in Glasgow colours, making his debut in victory away to the Dragons last February.
His first start came in the final round of the 2024/25 regular season, impressing with his physicality in defence despite a narrow defeat to Leinster at the Aviva Stadium.
He started the 2025/26 season in impressive fashion, claiming BKT URC Player of the Match honours in defeat to Benetton before scoring his first try for Glasgow a fortnight later in a bonus-point win over Ospreys.
Duncan has also represented Emerging Scotland this season, featuring in the squad’s clash with Tonga XV at Scotstoun last November.
“I’m buzzing,” Duncan told glasgowwarriors.org following the announcement.
“I’m so excited. It’s been a long process, but the labours have paid off and I’m really looking forward to getting stuck in.
“I’ve really enjoyed this season so far. My first start of the season against Benetton felt like the result of all the building blocks and effort you put in during pre-season, and while we didn’t get the result over there it felt like something I could really kick on from.
“Franco for me is one of the best coaches in the world. To be able to learn from him and the rest of the coaching team day in, day out is such a brilliant experience – Nigel [Carolan] with the attack, Roddy [Grant] and Scott [Forrest] with the breakdown and defence, these guys just give you so much detail and I’ve learnt so much already. You just pick up the knowledge from how they see the game.
“I just want to keep my head down, keep working hard and keep pushing to be involved – we’ve got a big run of matches coming up and hopefully I can be a part of it with this group.”
Head Coach Franco Smith added: “Macenzzie is a young player that we believe has real potential, and he has grasped his opportunities when they have arisen.
“His ability to perform well across all three back-row positions is an invaluable quality, in addition to his dynamism and physicality in both attack and defence.
“He is a young man who is keen to learn and develop to become the best version of himself, and we look forward to continuing to work with him.”