The news is further evidence of the Scotstoun-based club acting to secure its brightest talent at a time when the on-field focus is set firmly on reaching the end of season semi-finals.
The victory in the Liberty Stadium, a first ever for Warriors on Ospreys soil, puts Sean Lineen's men in the last of the play-off positions ahead of a crunch Firhill double-header against Aironi (Friday 23 March) and Cardiff Blues (Friday 30 March).
Reid, a powerful scrummager and dynamic presence in the loose, has made a consistent impact whether from the start or off the bench in his first season as a full professional.
Last Friday, he made a key defensive contribution in the last half hour to help the Warriors close out the win, almost exactly a year to the day since making his debut at the same venue.
The loosehead, who turned 25 on Sunday, was previously a standout performer for Ayr in the Premiership and British and Irish Cup.
Reid told www.glasgowwarriors.org: "I'm really pleased to have signed for another two years with Glasgow Warriors.
"I've loved the challenge of adapting to the professional environment, and I've learned a massive amount from working with, and talking to, quality players and coaches on a daily basis.
"I feel there's plenty more to come, and I'll continue to work as hard as I can to keep improving."
Gillies, meanwhile, has built on the grounding he received at Haddington and Heriot's to establish himself as a genuine contender for the Warriors number 2 jersey.
He started the season as part of the Elite Development system, but after proving his mettle in the away wins over Leinster and Cardiff Blues, earned a full professional contract last December.
The 23-year-old former Scotland under-20 and Club XV forward has now joined fellow Elite Development graduate Stuart Hogg in signing a long-term extension.
He said: "It's great to have my future sorted out. This is a terrific club and group of players, and there's obvious potential for us to grow on and off the pitch.
"Everyone at the Warriors is motivated to achieve success in the remainder of this season and over the next few years. I'm looking forward to being part of that, and to continuing to challenge for a place in the team."
Head coach Sean Lineen is delighted to have tied down the front row pair, saying: "In the contracting work we've done so far this season, we've shown a clear desire to reward players who have stepped up and proved they've really got something to offer at this level.
"Gordon and Finlay are two guys who we've been very impressed with both on and off the field, and they thoroughly deserve these new contracts.
"Coming from the club game, Gordon has shown what it's possible to achieve with the right attitude and skill set. He's an excellent ball carrier, his scrummaging has improved out of sight, and it's no exaggeration to say that he's now an integral part of the squad.
"Finlay has a terrific mindset: he's got an innate feel for the game and makes good decisions. He's a winner who's never satisfied; he knows he can get better as a player and he continually strives to achieve that.
"I'm extremely pleased to have another two guys signed - we're all excited about where this group can take the club."
Reid and Gillies are the 13th and 14th players to commit their long-term future to the club in recent months.
In addition, the Warriors have announced three major new additions for season 2012/13: wing/centre Sean Lamont, Tonga's World Cup star No.8 Viliami Ma'afu, and lock Tim Swinson, one of the most consistent second rows in the English Premiership who was Newcastle Falcons' Player of the Season last term.
The next game in the Warriors' bid to reach the RaboDirect PRO12 play-offs sees them face Italian side Aironi at Firhill on Friday 23 March (kick-off 7.35pm).
Tickets for the match are available NOW via www.glasgowwarriors.org, by calling 0844 800 3490 or in person at the Gordon Street and Sauchiehall Street branches of Greaves Sports our official retail partner.
Students are invited to celebrate the end of term with a great value £5 ticket - half the normal price.
Adult tickets bought online or over the phone in advance cost just £15 - a £5 saving on the match-day price.
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