Joshua, who defends his WBA, IBF and WBO heavyweight titles against Oleksandr Usyk at Tottenham Hotspur Stadium on Saturday, has been promoted by Hearn since turning professional eight years ago.
It is thought this weekend's contest was the last on Joshua's previous arrangement with Matchroom but the two parties have now come to an agreement that will cover the remainder of Joshua's fighting career.
"The foundations we have created are phenomenal and I can't wait to see what the future holds," Joshua said.
"In my humble opinion, what better place to be than Matchroom Boxing? I have heard that my signature was hot property. I'm happy where I am.
"A handshake is good enough for me, but the signature solidifies it and I'm happy where my signature is."
Earlier this summer Hearn ended a long-term partnership with broadcasters Sky Sports to move to streaming platform DAZN.
Joshua's showdown against Usyk will be screened in the UK and Ireland on Sky via pay-per-view, although DAZN has the rights in more than 170 other countries and territories worldwide.
It is as yet ambiguous what Joshua's new contract means for the TV rights after this bout.
"This is the fourth and final promotional agreement we have signed together, and I am honoured that AJ has confirmed his future with Matchroom," Hearn said.
"Just like we did from the debut, myself and the great team at Matchroom will continue to work relentlessly for Anthony in the many chapters that remain."