Kamara, 22, will be trained by Essex-based Tony Sims and is set to make his debut in October.
The Liverpudlian fought as a junior middleweight in the unpaid ranks and won seven national titles, including the Senior Elite Championship.
Last year at the World Boxing Championships in his home city of Liverpool, Kamara won a bronze medal, beating Canada’s Kuwardeep Manu along the way.
“After my decision to turn professional, my attention was firmly on who I thought was best to guide me to the very top of this sport,” Kamara said.
“Expect fireworks because I want to give the fans value for money every time I’m in the ring.”
Hearn added: “Kamara is one of the future faces of British boxing. This kid has got it all: he has got the looks, the personality, the power, and, above all, he can really fight.
“This young man is going to bring some major nights to Liverpool and, believe me, he is going to light up the world’s stage before long.”