The 25-year-old, who joined for a fee of €12m (£10.1m) plus an extra fee, flew to London on Tuesday before undergoing a medical and the move has now been officially announced.
Kehrer spent four seasons at PSG, having signed in 2018 from Schalke, and the centre-back has made 20 senior international appearances for Germany.
“I am very happy to sign for West Ham United,” Kehrer said. “It’s the best league in the world and I’m delighted to come and play in the Premier League.
“I spoke to the manager and he told me how he sees me fitting in at the club. My biggest goal now is to get into the team, fit in with the group and enjoy playing for West Ham.
David Moyes is desperate to bolster his defensive options, after new signing Nayef Aguerd was forced to undergo ankle surgery and he will miss at least the first two months of the season.
The Hammers had only one fit centre-back for their opening two games of the season, defeats to Manchester City and Nottingham Forest, meaning Ben Johnson had to replace Kurt Zouma. Craig Dawson remains out with a thigh problem and Angelo Ogbonna is still recovering from a long-term ACL injury.
Kehrer’s arrival comes at a good time and he becomes West Ham’s sixth senior signing of the window, with the club spending more than £100million as Moyes look to bolster a squad that was worrying for much of the season. last season.
“I am really delighted to welcome Thilo to West Ham United,” said Moyes. “He’s a talented player, who can play in a number of defensive positions, adding strength and depth to our current options.”