The 30-year-old, released by Nottingham Forest at the end of last season, has signed a deal until the 2029-30 MLS season.
“It feels incredible to join the Earthquakes,” said Gunn. “Coming off the World Cup, which was an unbelievable experience, I’m just really excited and grateful for the opportunity to come to San Jose and show the best version of myself.
“We’re in a really good position for the play-offs, so hopefully we can focus on that with the right mentality.”
Norwich-born Gunn – son of Canaries legend Bryan – came through the ranks at Carrow Road, but left to join Manchester City in 2011. He spent a season on loan at Norwich in 2017-18 before joining Southampton for £13.5m.
He returned to Norwich on a permanent deal in 2021, leaving at the end of the 2024-25 campaign, having made 160 league appearances over his two spells.
“We’re pleased to sign a quality goalkeeper in Angus Gunn with English Premier League and international experience, most recently as a starter at the World Cup,” said Earthquakes sporting director and head coach Bruce Arena.
“We’re looking forward to integrating him into the club for the second half of the season and welcome him to San Jose.”