The 23-year-old has signed a five-year contract with Southampton and has joined for an undisclosed fee.
Walker-Peters impressed while on loan at Saints and Ralph Hasenhuttl saw him as the man to solve the club’s issues at right-back in the long term.
“It was not easy for Kyle when he arrived here. He needed some time to adapt to our style of play, and then we had this period where we could not be together as a team,” Hasenhuttl said in a statement released from the club.
“He is a very good fit for our style. He is a young, intelligent player, and he is very good on the ball, with good quickness and an ability to play this intense style that we like.
“I am very pleased we have been able to bring him back as our player, as this is a position that we have been looking to improve in and Kyle does this for us. I think he can develop his game even more here too.”
Walker-Peters is similarly pleased to confirm his much-rumoured move to Southampton.
“The club definitely fits the way I like to play, and I hope that people were able to see that during the last month or so of the season,” Walker-Peters is quoted as saying in the same club statement.
“I feel like I’ve already developed in the time I’ve been here, and that’s a big part of wanting to stay too. Obviously, it’s a club with a great reputation for improving young players and, personally, I’ve found it really valuable working under the manager, with his ideas on the game and what he expects from you as an individual.
“I think the way we finished the season gives us real optimism about where we’re heading too, and it just feels like a really good place for me to keep developing as a player and make the best out of what I have.”
Former Southampton captain Pierre-Emile Hojbjerg has went the other way to Spurs in a separate transfer.
When does the summer transfer window open and close?
The summer transfer window opened on 27 July and closes at 23:00 on 5 October.
A domestic-only window for trades between Premier League and EFL clubs will run from 5 October until 16 October at 17:00.