Liverpool stated on its website that the Japanese international would travel to Saint Mary after the agreement with Southampton on the last day of the transfer window.
Minamino did not find his chance to participate with the Reds constantly in light of the brilliance of the front trio, Mohamed Salah, Sadio Mane and Roberto Firmino.
Minamino has participated in 31 matches since joining from Red Bull Salzburg in January 2020, and has scored 4 goals in various competitions.
Southampton are 11th in the Premier League and face Manchester United on Tuesday.
Meanwhile, Liverpool are third on the table and prepare to take on Brighton on Wednesday.