Joshua secures IBF world title shot against Martin
The current British and Commonwealth champion has enjoyed an explosive start in the pro ranks, winning his first 15 fights by knockout in just 32 rounds.
The American, who won the title in January against Ukranian Vyacheslav Glazkov, will be fighting outside of the United States for the first time.
"Fighting for the heavyweight world title has been a dream of mine since I turned professional," said Joshua. "I feel privileged to have the opportunity to turn that dream in to reality."
"Not only that, having the chance to fight for it in my home town at The O2 is unbelievably exciting."
"Charles Martin is a great fighter and a hungry competitor so I am going to have to produce the performance of my career to claim that belt."
Martin represents a serious step up in class for the 2012 Olympic gold medalist, having won 22 and drawn one out of 23 contests – 21 by knockout.
He said: "I told my team I wanted the best challenger possible for my first defence and Anthony Joshua's name kept coming up. I'm coming to the UK to make a statement that I am the best heavyweight in the world and no one is taking my title."
"I'm world champion, so that doesn't mean just sit back and make easy defenses in the US, it means facing the biggest challenges out there."
"I respect Anthony Joshua and everything he has accomplished, but on April 9 he's getting knocked out."
Joshua's promoter, Eddie Hearn, said there was no holding his fighter back once the opportunity to fight for a world title presented itself.
"He wants to give the fans something to get excited about and he wants to become a great, and even though the decision among the team took a week or so, I believe his mind was already made up from the moment I asked him."
"It's a complete honor to promote an event of this magnitude. I believe it's one that will go down in the history of the sport."
The fight presents Joshua with the opportunity to join Tyson Fury as a British heavyweight world champion.
Fury vacated the IBF belt at the end of last year, allowing Martin the chance to beat Glazkov in New York and claim it.
The current WBA and WBO title holder was expected to face a rematch against Wladimir Klitschko later this year, but Fury's Tweet over the weekend about an 'urgent meeting in London' has caused speculation that a fight against David Haye could be on the cards.
Some massive news coming soon, had to come to London for an urgent meeting about a massive fight,TBA very soon, u will not believe who!!!!!!— Gypsy King (@Tyson_Fury) February 13, 2016