The 25-year-old, who is recovering from a foot injury, enjoys a prolific strike-rate at the Scotstoun club with 31 tries in 60 appearances.
Horne follows in the footsteps of fellow scrum-halves Jamie Dobie and Sean Kennedy - as well as fellow Scotland internationals Scott Cummings and Sam Johnson, and openside Tom Gordon - in extending his stay with the Warriors.
The Dundee-born half-back came through the FOSROC Scottish Rugby Academy and made his debut for the Warriors at home to the Ospreys in November 2016.
He has scored six tries in 14 Scotland appearances, including a hat-trick against Russia at the 2019 Rugby World Cup in Japan, where he became just the fifth Scotland player – and the first in 12 years - to cross for a treble on the sport’s biggest stage.
Glasgow did not reveal the length of the contract.
“This is a club I’ve grown up supporting and I’ve made some great memories being a part of this team,” Horne told glasgowwarriors.org.
“I’m champing at the bit to get back playing. Recovery is going really well, and I can see the light at the end of the tunnel.”
Glasgow head coach Danny Wilson said: “George is very passionate about Glasgow and he shows that every time he takes the field.
“Along with Jamie, Ali [Price] and Sean, George’s signing gives us great depth with four outstanding Scottish scrum-halves to pick from.”