Ten Hag said: “It is a great honour to be appointed manager of Manchester United and I am hugely excited by the challenge ahead. I know the history of this great club and the passion of the fans, and I am absolutely determined to develop a team capable of delivering the success they deserve.
“It will be difficult to leave Ajax after these incredible years, and I can assure our fans of my complete commitment and focus on bringing this season to a successful conclusion before I move to Manchester United.
”Man United football director John Murtough added: “During the past four years at Ajax, Erik has proved himself to be one of the most exciting and successful coaches in Europe, renowned for his team’s attractive, attacking football and commitment to youth.
“In our conversations with Erik leading up to this appointment, we were deeply impressed with his long-term vision for returning Manchester United to the level we want to be competing at, and his drive and determination to achieve that.
“We wish Erik the best of luck as he focuses on achieving a successful end to the season at Ajax and look forward to welcoming him to Manchester United this summer.
”Man Utd have been in the hunt for a permanent successor to Ole Gunnar Solskjaer after the Norwegian was relieved of his duties at the end of November.
Ten Hag comes in as the fifth permanent manager at Old Trafford since Sir Alex Ferguson called time on his career in 2013.