The German took over the Ligue 1 side in June 2018 and led them to the French title this season.
However, PSG again struggled to make the impact they wanted in the Champions League as they went out to Manchester United at the last-16 stage.
PSG were also beaten in the French Cup final as they lost to Rennes on penalties.
“I’d like to thank the chairman and the whole club for their trust in me and my staff,” said Tuchel, 45.
“This only reinforces my ambition to bring this team to the very top through hard work.”