The 27-year-old's deal ties him to Warriors until May 2019, having joined in 2010.
Pyrgos, capped 18 times by his country, told Glasgow's website he had spoken with Dave Rennie, who will replace head coach Gregor Townsend next year.
"He told me about his vision for the club and his rugby philosophy and it's exciting," said Pyrgos.
"To have someone of Dave's quality coming in is brilliant for the club.
"I love everything about Glasgow Warriors and the club means a huge amount to me.
"This is my seventh year at the Warriors and winning the Pro12 two years ago has been the standout moment.
"I'm excited for the future here and we'll be working extremely hard to continue to compete for trophies every season. I believe we have a squad capable of doing that and that's the main reason I wanted to stay."
Townsend, who will become Scotland head coach next summer, added: "It's brilliant news for the club that Henry has signed for another two years.
"He is one of our leaders and has developed a huge amount in his time at the club. Now he is helping the club continue to improve and evolve on and off the pitch.
"There is a lot more to come from him on the playing side and we are really fortunate to have such a high quality group of scrum-halves right now."

Ben, from Sheffield, was 21 months old when he disappeared on 24 July 1991.
Detectives said they would be "lifting all the earth" at the second site, 750m from where he was last seen and close to where the dig started last month.
They are investigating claims Ben may have been accidentally run over by a digger driver 25 years ago.
Officers are working on the theory that Konstantinos Barkas, who died of cancer in 2015, might be responsible for Ben's death.
Ben vanished from a farmhouse, which his grandfather was renovating, in the village of Iraklis.
Continued searches near the farmhouse were drawing to a close and the rest of the team will be focusing their efforts on the second site, police said.
Det Insp Jon Cousins said there was compacted material deposited over the last 30 years and the team "will remove this layer in the same [way] they excavated the first site".
Mr Cousins said: "I have made a decision that we're extending our stay here.
"We are going to be doing this to give me the confidence that I've done everything I can.
"The team are 100% behind this. And every single one of them, including the volunteers, are adamant that they are staying for this period of time. It's got to be done."
The team would remain on site for "at least two or three days", he said.
A team of 19 South Yorkshire Police officers, forensic specialists and an archaeologist have been excavating the area for nearly two weeks as a result of a television appeal in May, which brought the theory about Mr Barkas to the attention of the force.
Scotland scrum-half Henry Pyrgos has signed a new two-year contract with Glasgow Warriors.
[NEXT_CONCEPT]
Police searching for missing toddler Ben Needham on the Greek island of Kos have said they are extending their stay to continue exploring a second site.