The back-row pair have penned new two-year contracts, which will keep them at Scotstoun until at least May 2016.
Harley joined Glasgow in 2010 and has made 93 appearances for the RaboDirect PRO12 side.
The 23-year-old has become a regular feature in the Warriors pack and won his first Scotland cap in the 2012 summer tour to the South Seas, scoring a try on his debut against Samoa. He has gone on to make five appearances for his country.
Rob Harley said: "I've really developed as a player over the last four years, getting regular game time at the Warriors and playing for Scotland.
"I feel like this is the perfect place for me to continue my development, working with a great group of players and coaches."
Holmes joined the club last summer on a one-year deal and has featured regularly this season, making 17 appearances.
The 28-year-old, who celebrated his birthday yesterday, put in a man of the match performance in the Warriors home win against the Exeter Chiefs in the Heineken Cup and earlier this year made his Scotland A debut in the draw with England Saxons.
Tyrone Holmes said: "It was a great decision to come to Glasgow in the summer and I'm delighted to be staying for another two years.
"My father was born in Peebles and he is so proud of what I've achieved in Scotland this season. I've already sent my Scotland A shirt back to him in South Africa."
Glasgow Warriors head coach Gregor Townsend said: "It was really important for us to get Rob (Harley) and Tyrone (Holmes) re-signed as the back-row is a very competitive area for most teams.
"Rob is a very consistent player and is extremely hard working. He is always prepared to put his body on the line in training and in games.
"He's usually one of the players who plays the most rugby for us and this season is no exception.
"Rob is developing his running game, his catch-pass skills and his line-out ability is also improving, so he's got a great future ahead of him.
"Tyrone has been great for us since joining in the summer. He's really given us competition at openside and has pushed Chris Fusaro to playing at his best.
"Tyrone is a low tackler and a very committed player, and has played very well for the club, with the Exeter Chiefs match at Scotstoun being a standout.
"As we approach the most important part of our season, it is a boost to have secured Rob and Tyrone for the next two seasons."
Glasgow Warriors face Ulster in a top four encounter at Scotstoun Stadium this Friday (18 April, kick-off 7.35pm).
The capacity of Scotstoun has been increased to around 10,000 for the remainder of the season and tickets for Friday's game are available from www.glasgowwarriors.org or by phoning the ticket office on 0844 800 3490 (Monday to Friday, 9am-5pm).
The ticket office at Scotstoun will be open on Friday from 10.30am and tickets will be available right up until kick-off (subject to availability).
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