The 34-year-old has impressed this season, making 18 appearances for the Capital One Cup finalists.
The German's original deal was due to expire at the end of this season but he has now committed himself to the Swans until 2015, with the option of a further year.
Tremmel, who joined Swansea from Red Bull Salzburg in August 2011, said: "Since the first day I joined this club, I knew something special was happening.
"I have been at a number of clubs, but the feeling here between the players, staff and supporters is different. I feel very, very good here. Of course, last season I didn't play the amount of games I had hoped for, but this season has been a completely different story on the pitch for me.
"I have played in a lot more games and big matches against the likes of Manchester City, Chelsea, Arsenal and Liverpool to name but a few. I think it has been good for myself and the supporters. I've been able to build momentum with a consecutive run of games this season, while the fans can now see what I am capable of.
"I am contributing a lot more, which is great, and when the opportunity came along to sign a new deal here I was very happy to do that.
"The club has been on a remarkable rise over the last few years, and it really is a nice story - I was keen to be a part of that story, so the new contract is great news for me because I feel I have a lot more to give this club."
Tremmel follows the likes of Leon Britton and Garry Monk in committing their future to City recently, while Michel Vorm, Ashley Williams, Ben Davies, Neil Taylor, Wayne Routledge and Michu have also penned new contracts this season.
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