Joe Aribo signed a four-year deal with Saints.
The 25-year-old Nigeria international joins for a fee reported to be about 6 million dollars, rising to 10 million dollars with add-ons.
Aribo scored in last season's Europa League final defeat and helped Rangers win the Scottish Premiership in 2021.
The club has a lot of history, according to Aribo.
The premier league is the top league in the world. I've been watching it for a long time. I've always wanted to play here and show what I can do.
It's a dream come true. I've wanted to be here since I was a child and it's great to be here now.
The manager said he was very pleased to add a player with many qualities.
Joe has the ability to bring energy and creativity to the table. It's important for a manager to feel comfortable in so many different positions because it shows he has a high level of football intelligence.
He has played at a very high level in his career and his performances in the Europa League prove he has the ability to play in the premier league. He wants to show everyone he can do it, and he is hungry to do it.
The Rangers boss told Sky Sports that Aribo was going to leave the club.
He has done a great job for this club.
Aribo, who had one year left on his Rangers contract, is the fifth summer signing for the Saints.
On our dedicated page, you can find all the latest football transfers.