The Stewartry RFC product has made 81 appearances - as well as crossing for 16 tries - for the Warriors to date, having made his professional debut against the Southern Kings at Scotstoun back in 2017.
McDowall's 2023/24 campaign saw the centre play an integral role to Glasgow's BKT United Rugby Championship title victory; having featured in 17 of Glasgow's 18 regular-season matches, he also picked up the Denholm Energy Services Players' Player of the Season trophy at the club's end-of-season Awards Dinner in recognition of his sterling campaign.
Having captained the Warriors for the first time in a 40-26 win over Perpignan in January 2023, the 26-year-old continued to deputise for club captain Kyle Steyn during 2023/24, including in back-to-back victories over the Dragons and Benetton earlier in 2024 - winning Player of the Match in both fixtures.
His form in a Glasgow shirt saw him earn a senior Scotland debut ahead of the 2023 Rugby World Cup, pulling on the dark blue jersey for the first time against Italy at Scottish Gas Murrayfield.
McDowall's leadership qualities were also recognised by the Scotland coaching team, first handing him the co-captaincy in July's win over Canada in Ottawa, before the centre was asked to lead the team against Portugal at Scottish Gas Murrayfield earlier this month in a performance capped off by running in an interception try from halfway.
A Scotland international at U18, U20 and A level, he also helped Ayr RFC to a league and cup double in the 2018/19 campaign in addition to his outings in a Glasgow shirt.
"I'm really pleased to renew my contract," McDowall told glasgowwarriors.org.
"It's the club that I grew up supporting and a club that I take great pride in representing on and off the field.
"I'm loving my rugby here. The brand of rugby we play is a really exciting one, and its one that I hope the fans enjoy watching as much as we enjoy playing!
"Taking on a leadership role is also definitely something I've enjoyed in the last year or two. There are so many great leaders at the club currently, which really helps to drive the standards within the club.
"I want to play my part in helping this group defend the URC title, beginning this Friday, as well as help push us forward to challenge in Europe as well. I can't wait to get back out there on Friday night if selected."
Head Coach Franco Smith welcomed the news, adding: "Stafford has developed into a key leader in our playing group, and is someone who regularly drives our standards and our values on and off the field.
"His skillset enables him to contribute effectively both in attack and defence, whilst also bringing out the best in the players around him.
"He has fully bought into the journey that we are on as a club, and is fully committed to helping this group achieve its potential."