Unai, 46, previously spent three seasons with Sevilla, leading them to an unprecedented three consecutive Europa League titles, establishing the club as a major force in the Spanish league.
Announcing the appointment, chief executive Ivan Gazidis said: “Unai has an outstanding track record of success throughout his career, has developed some of the best young talent in Europe and plays an exciting, progressive style of football that fits Arsenal perfectly. His hard-working and passionate approach and his sense of values on and off the pitch make him the ideal person to take us forward.
Majority owner Stan Kroenke said: “We’re delighted to welcome Unai to Arsenal. He’s a proven winner. We’re confident that he is the right person for the job and that he will work to deliver the triumphs our fans, staff and everyone who cares about Arsenal want.
“Several things stood out during his interview and the entire process; his football knowledge, energy, determination and love of the game. His familiarity with our club and our players, the Premier League and the game in Europe were all very impressive. He shares our vision to move forward, to build on the platform created by Arsène Wenger and help this club enjoy greater success.”