After 10 years with Bayer, Tah has joined league rivals Bayern, where he will provide defensive support.
Rumours of a move to Bavaria had been circulating for several weeks. Tah's transfer became more tangible on Wednesday following reports of his medical and his presence at the Bayern HQ.
The defender has committed himself to Bayern until June 2029. In the German club's press release, he said he was "very happy to be at FC Bayern.
"I want to take on responsibility here and work hard every day so that we’re successful as a team and win lots of trophies together," Tah added.
A youth product of Hamburger SV, Tah also played in the senior team before moving to Leverkusen in 2015. At Bayer, he played 402 games.
Called up to the German national team in 2016, he has made 35 appearances for the Mannschaft to date.
Bayern CEO Jan-Christian Dreesen said of the signing: "We’re delighted to welcome Jonathan Tah to FC Bayern.
"As an experienced international and leader, he brings the consistency and quality that will strengthen our defence. He’s a real gain for us - and he’s also proven that he can win titles."