The talented trio have signed up to stay in Scotland's number one city until at least the end of May 2014, giving the Warriors a great pre-match boost ahead of the RaboDirect PRO12 visit from Dragons on Friday (kick-off 7.30pm).
The three players are already prominent figures in the Scotstoun set-up, and the retention of their services was today described as "vitally important" by chief executive Kenny Baillie.
He told the club's online home, www.glasgowwarriors.org: "Chris, Ryan and Duncan have proved they are key players for Glasgow Warriors, and we're delighted they see us as club where they can achieve their aspirations and continue their individual development.
"It's fantastic news to have secured the players so early - it sends out a positive message to our supporters and allows the players to focus on continuing to deliver quality performances.
"Glasgow Warriors are committed to improving results on and off the field. In the past three weeks, we've taken great heart from the early contracting of three of the most talented individuals in our squad, the announcement that we will be using Scotstoun Stadium as our playing base from next season, and the excellent away wins over Cardiff Blues and European champions Leinster.
"The raft of new sponsors we have recently confirmed provides further evidence that the club is moving in the right direction.
"It's great that the players are excited by our plans, and their contribution will be vital as we work to ensure the club fulfils its undoubted potential."
Fusaro joined the Warriors on his first professional contract last summer, shortly after being called up to the Scotland A squad for the IRB Nations Cup in Romania. A combative openside flanker, the 22-year-old has played a leading role in the first month of this season's RaboDirect PRO12 campaign.
The former Heriot's man said: "It's really pleasing to know I'm going to be part of Glasgow Warriors for the foreseeable future. I've loved my time at the club so far, and have learned a massive amount from being around quality international players.
"We've got a young and hungry squad, and that's going to stand us in good stead for what should be a really positive phase in the club's development."
Loose-head prop Grant concurred, saying: "There's no doubt that these are exciting times for the Warriors. The guys are really taken with the prospect of playing our games at Scotstoun Stadium next season, and I want to play my part in helping the club continue to thrive.
"There's a real sense of common purpose in the Glasgow dressing room. I feel like I've been part of the group for a long time despite only having signed last summer, and I think that speaks volumes for the atmosphere and working environment."
Grant, 25, has gone from strength to strength in the blue and black since joining from rivals Edinburgh Rugby in June 2010.
Alongside producing a string of powerful displays for the Warriors, the former Border Reivers man was a central component of the Scotland A side that maintained a 100% record throughout the 2010/11 season, and duly won a call up to the wider Scotland squad for the Rugby World Cup.
Stand-off Weir, still only 20, is another who looks set for a bright future. A product of Cambuslang and Glasgow Hawks, the pivot has quickly established himself as a compelling presence in the Warriors camp since stepping up to the professional tier in 2010.
The Scotland A fly-half said: "As a Glasgow boy through and through, I take huge pride in wearing the Warriors jersey and there's no better place for me to continue to come on as a player.
"With Ruaridh Jackson, Scott Wight and Colin Gregor all now in the squad, there's plenty of competition for places at stand-off, but that's often the most effective way of getting the best out of each individual. I'm up for the fight of securing a place in the team and helping the club achieve success."
Head coach Sean Lineen has welcomed the re-signings, telling www.glasgowwarriors.org: "It was a priority for us to get these guys tied down early in the season. They've all really grasped the opportunity to become influential players for Glasgow Warriors, and the other coaches and I will be working hard with them to make sure they continue to fulfil their potential."
Tickets for the Dragons game are available via www.glasgowwarriors.org, by calling 0844 800 3490, in person at the Greaves Sports stores on Gordon Street and Sauchiehall Street, or at Firhill on the night. Adults £15 (£20 after 5pm on Thursday); students/senior citizens £10; under-18s £5.
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland