The 25-year-old international from Nigeria has signed a four-year contract.
Aribo will be acquired by Southampton for an initial fee of £6 million, plus potential future add-ons.
He moves to St Mary's in this transfer window along with goalkeepers Mateusz Lis and Gavin Bazunu, defender Armel Bella-Kotchap, and fellow midfielder Romeo Lavia.
Aribo, a versatile midfielder who played in central midfield, attacking midfield, down the right, and closed the season up front for Rangers under Giovanni Van Bronckhorst, has been added to Southampton's team.
Aribo said:
'It's an amazing club with a lot of history here, and it's a good plan with what's to come next. I'm really excited for the journey.'The Premier League is the best league in the world. I've been watching it since I was a young boy, it's always been a goal for me to play here and show what I can do on this stage.'It's an amazing feeling, a dream come true. This is where I've wanted to be since I was a child growing up playing, so to say that I'm here now is really exciting.'
Speaking on that, Southampton manager Ralph Hasenhuttl said:
'Joe is a player with many qualities to his game, and we are very excited to welcome him to the squad in time for the pre-season trip to Austria.'We believe Joe can bring energy and creativity to our side. Feeling comfortable in so many different positions is very helpful for a manager and shows he has a high level of football intelligence, with the ability to take on new information quickly.
Aribo moved to Southampton following a standout season in which he was one of Rangers' most used players, making 57 appearances, scoring nine goals, including one in the Europa League final against Eintracht Frankfurt, and assisting on another ten.
