The Poland defender signed for the Gunners on Monday from Spezia.
Manager Arteta said: "It's great that Jakub is joining us. He's a young versatile defender who has shown huge potential and qualities with Spezia in Serie A, and also at international level with Poland.
"Jakub is a player who will give us strength and quality to our defensive unit. We welcome Jakub and his family to Arsenal and look forward to working with him."
Technical director Edu said: "We're delighted to have completed the signing of Jakub Kiwior. He's a young talent who we've been monitoring for a while now. We are now all looking forward to working with Jakub and seeing his continued development with us. We welcome Jakub to Arsenal.