Under the terms of the deal the Baltimore company will continue to supply the IBF world heavyweight champion with his in-ring apparel. Joshua will also lend his image to Under Armour's future marketing campaigns.
“I am delighted to be committing my long-term future to Under Armour,” said Joshua. “It is a partnership that has been incredibly successful to date, the brand has helped me increase performance with custom products and new technologies.”
Chris Bate, Under Armour's managing director for Europe, said: "“During his preparation for the Klitschko fight and beyond, we will equip Anthony with our most innovative performance products including our Threadborne technologies and Connected Fitness footwear and platforms. We are thrilled to have Anthony as part of the Under Armour team.”
The London 2012 Olympic gold medallist first partnered with Under Armour in February last year after agreeing a three-year deal with the brand ahead of his highly anticipated title shot against Charles Martin.
Now the 27-year is preparing to Wladimir Klitschko in April in a bout which is receiving huge media attention.
Freddie Cunningham, the head of Joshua's management team, added: “The deal is a real landmark not only for Anthony but also for British sport. He is attracting major interest internationally and this is his first real step on to the global scene commercially. The brand is a perfect fit for Anthony, young, inspirational and fast moving."