Foketi, 31, was born in New Zealand before his family moved to Australia.
He played for Australia Under-20s and made his Super Rugby debut for Melbourne Rebels in 2014 before leaving to play for French side Bayonne later that year.
Foketi returned to New Zealand where he played a couple of seasons for Bay of Plenty in the Mitre 10 Cup competition before linking up with the NSW Waratahs from 2018 until 2025.
Foketi was given his first Australia cap as a replacement in the 29-28 defeat against Wales in Cardiff in November 2021, before appearing three times in the 2023 World Cup in France.
Foketi played for the First Nations and Pasifika XV against the British and Irish Lions on the 2025 summer tour of Australia before leaving Waratahs later that year.
He joined Hamilton-based Chiefs for the 2026 campaign and will be involved in the Super Rugby final next weekend.
Foketi was instrumental in the semi-final win against Crusaders with three try assists, the joint most of any centre in a Super Rugby game since 2020.
“This is another great bit of news for the club and our supporters,” said Ospreys head coach Mark Jones.
“Lalakai is an experienced international who can immediately make a real contribution for us on and off the field.
“He’s a real all-rounder at centre with what he can offer on the ball and in defence, and we feel he will add even further quality to our already talented group of centres.
“He’s got a few points of difference that will bring a new dimension to our attack, and we’re excited to utilise that.”