Tuchel took charge of the club only days before they returned to the Bundesliga in 2009 after Jorn Andersen was dismissed.
In his first year, he led them comfortably to safety before setting a new club record for consecutive wins at the start of last season, sealing a place in the Europa League despite a late slide down the table.
This year, he has saved them from relegation again with several games to spare and his achievements have been rewarded with a new contract, which he signed on Thursday.
"The management of Mainz are offering me the opportunity to mould the identity of this club and, together with my coaching team, develop it continuously," said Tuchel on his club's website.
"We would like to establish Mainz as a sustained Bundesliga side.
"The feeling of being valued that I have had from the club and the fans in recent years is something special.
"Therefore, signing a new contract is just a logical consequence of this close, faithful cooperation."
Tuchel has even managed to emerge from the shadows of one of his predecessors Jurgen Klopp, now coach of Borussia Dortmund, who first brought Mainz back into the top flight in 2004.
"Thomas Tuchel is an absolute expert and, with the way he lives and breathes football, he is just the right coach for Mainz," said the club's general manager Christian Heidel.
"He is the most important piece in our puzzle for the future."
Tuchel's record as Mainz coach reads 39 wins, 27 draws and 35 defeats.