Tuchel replaced Unai Emery on a two-year deal last summer and helped PSG successfully defend their league title this season.
Although the French champions made a fine start under the German tactician, their season nosedived as they were dumped out of the Champions League at the last-16 stage for the third straight year and also failed to retain the two domestic cups.
However, the PSG hierarchy have chosen to retain Tuchel, offering him new terms.
“I’m delighted to extend my contract and commitment to Paris Saint-Germain.
“I’d like to thank the chairman [Nasser Al-Khelaifi] and the whole club for their trust in me and my staff.
“This only reinforces my ambition to bring this team to the very top through hard work. I’m also very touched by the backing of our supporters, and I’m sure that the best is yet to come for our club,” Tuchel told the club’s website.
