The former Ulster player is Glasgow's joint top try-scorer this season, crossing the line five times for the RaboDirect Pro12 side.
The Nashville-born winger also won a Scotland squad call-up ahead of the EMC Test series, qualifying through his Glasgow-born mother.
"I said when I joined Glasgow that it was a little like coming home because of the family connection and I'm really settled here," Seymour said.
"The way the squad and team are developing is a massive factor in staying on because the players and coaches here do believe that we're building towards something special.
"It's an exciting place to be at the moment and even though the results don't always go your way, we know we're headed in the right direction.
"I came here to play regular rugby and to get that call-up to the Scotland squad was a real vindication of the hard work though I know, given the talent that is now in the Warriors squad, that I have to keep at it and keep trying to get better."
Seymour's contract extension comes ahead of their double-header against Edinburgh, which starts in Glasgow on Friday night.
Fifth-placed Glasgow go into the match seven points ahead of their rivals.
Seymour added: "The game against Edinburgh this Friday at Scotstoun is massive for us as a club, not just because of the intensity of the rivalry, but for our season and for our position in the league it's vital we do everything we can to pick up points."