Arsenal have named Gazidis as new chief executive in a statement this morning to the Stock Exchange.
Gazidis, a qualified solicitor and keen amateur player, said: "I have been privileged in my 14 years with MLS to have worked with, and for, some of the best sports executives and owners in the world, whose vision, commitment and expertise have taken the league from strength to strength and provided a solid platform for its future growth.
"I am delighted to be offered the opportunity to bring that experience to bear at Arsenal - a club rich in heritage and tradition, that is superbly positioned for success in the modern era.
"I relish the prospect of working with the key stakeholders to further propel the club forward.
"It is nearly 15 years since I left the UK but I'm very much looking forward to returning in January."