The German stopper signed a two-year contract at the Liberty Stadium in August 2011 following a successful trial with the Swans.
Tremmel had previously played in the Bundesliga for Hannover, Hertha Berlin and Energie Cottbus before a stint in Austria with Red Bull Salzburg, where he featured in their Europa League campaign.
He joined up with the Swans during their Austrian training camp in July 2011, and featured in the friendly match with the United Arab Emirates' Olympic team.
Brendan Rodgers then brought Tremmel to South Wales to take another look at the former Bayern Munich trainee, who played in the friendly victories over Celtic and Real Betis at the Liberty before joining on a free transfer.
He made one appearance in the Premier League – a 2-0 defeat at Stoke – while he also featured in FA Cup matches against Barnsley and Bolton.
However, Tremmel played a crucial part in Swansea's success during the 2012/13 season.
Following an injury to Michel Vorm in October 2012, Tremmel was thrust into first-team action, going on to make 21 appearances in all competitions - including playing every minute of the Swans' Capital One Cup run.
The German also featured 22 times in 2013-14 as the Swans reached the last 32 of the Europa League and finished 12th in the top flight.
Made six appearances in the 2014-15 campaign, with four coming in cup competitions.
Initially left the club after his contract expired in June 2015, only to return to the club two months later after penning a two-year deal.
He joined Werder Bremen on loan in January 2016, but failed to make an appearance for the Bundesliga club.