The Spain international moves to the Gunners for a fee close to £60m. He has signed a deal for an undisclosed length. Zubimendi has been handed the No36 shirt.
Zubimendi said, “This is a huge moment in my career. It's the move I was looking for and one I wanted to make. As soon as you set foot here, you realise how big this club and this team are.
“I set my sights on Arsenal because their style of play is a good fit for me. They have shown their potential recently and the best is yet to come.”
Gunners technical chief Andrea Berta said: “We are so happy to bring Martin to Arsenal and have a lot of pride in finalising this transfer. Martin was a key target for us and we all know that he is a perfect fit for our squad with the high quality he has.
“We welcome Martin and his family to the club. We look forward to him settling in with his teammates and are very excited to see him playing in an Arsenal shirt.”
Manager Mikel Arteta added: “Martin is a player who will bring a huge amount of quality and football intelligence to our team. He will fit in really well and he has all the attributes to be a key player for us.
“The standard he has consistently performed at over the last few seasons for both club and country is exactly why we are so excited to have him with us. We all welcome Martin and his family to the club.”