He's the unified champion of his division at 28 years old and 21 fights into his career.
Two of the three judges scored it 118-110 in Joshua's favour with the third giving it to the London Olympic champion 119-109.
While Parker was busy with his jab throughout and moved and defended well, Joshua used his superior reach expertly and was also the fighter coming forward throughout the majority of the bout.
Joseph Parker reacted humbly in defeat, simply saying: "Today I got beaten by a better champion, a better man. Thank you all for the opportunity". He wants one. I always tell people that when I'm in the ring, then I'm the "Bronze Bomber" and with him, it's so insane, I don't really care. It was a good experience being here.
"Of course. I'm young, fit and strong". I'm fit to go more rounds.
As Parker's mother looked on from ringside, Joshua took charge. "I want one. I really do", Wilder said, referring to himself in his "Bronze Bomber" ring persona.
Parker swallowed a solid Joshua jab to begin the fourth and seemed briefly troubled, but the rest of the round was a non-event apart from a cuffing left hook by the Englishman which briefly checked Parker's balance.
Both are now undefeated ahead of the meeting in Cardiff, with Joshua weighing in six pounds heavier than Parker, which hasn't come as a surprise to many.
"Do I want to become undisputed heavyweight champion of the world?" Not only is he the sole world champion with a 100 percent knockout rate (20 KO's in 20 professional fights), but his Fight of the Year win over Wladimir Klitschko last April vaulted him to the next level of stardom.
Hearn added: "I think it has to happen in 2018 otherwise we are going to hit some major problems with the politics and the mandatories (mandatory defences of the various belts)".
IBO and now the WBO heavyweight titles after Saturday's decision win over Joseph Parker.
Wilder is 40-0 with 39 career knockouts.
Joshua added: "That is 21 professional fights with six world title fights in it". Namely Wilder, or mandatory WBA challenger Alexander Povetkin, who beat David Price in the undercard. "UK and Great Britain boxing is on the map and we are representing".
New Zealand's Parker, 26, lost a title he defended twice after winning it by edging American Andy Ruiz by majority decision in December 2016. "We can do it here around Wembley [Stadium in London] or Cardiff". We are staying right here. You don't make a fight by being a Twitter warrior.