The Ukrainian won the WBA (Super), IBF, WBO, and IBO heavyweight titles by defeating AJ via unanimous decision with scores of 117-112, 116-112 and 115-113.
Usyk was by far the superior of the two boxers and he thoroughly deserved to win the fight.
"This means a lot to me", The Cat said after the bout.
"The fight went exactly the way I expected it to go. There was times when Anthony pushed me hard but nothing special. I had no objective to knock him out.
"My corner pushed me not to do that. My trainer said no and to stick to my job.
I've been working so hard since January. It took me some half a year. I miss my children. I want to go home. I'm not thinking about the rematch. You didn't see the best Usyk. I can be much better.
Joshua is one of the best heavyweight boxers in the world but never really seemed to make much of a comeback during yesterday's fight.
After the bout got over, the Brit was taken to hospital and is feared to have suffered eye socket damage.
Usyk handed Joshua only the second defeat of his career and maintained his 100% record, winning 19 out of 19.
Having previously been the unified cruiserweight champion as well, the Ukrainian is now a world champion in two weight classes.
He also joins Evander Holyfield and David Haye in the list of boxers who have been the unified cruiserweight champion as well as the heavyweight champion.
Joshua's defeat to Usyk means that the chances of a fight between him and Tyson Fury look very slim. T
he 31-year-old, however, will have a chance of avenging his defeat as there will be a rematch between him and the Ukrainian next year.