The 30-year-old was unbeaten in 20 fights leading up to the 'All or Nothing' showdown with New Zealander Parker and stunned the crowd with a scintillating comeback in the 11th round.
Despite suffering a flurry of punches throughout the contest that left him seemingly behind on points, Wardley landed one huge hook after another on Parker to leave former world champion and pre-fight favourite stranded on the ropes.
It gave referee Howard Foster no option but to end the bout prematurely.
Wardley, who has 19 knockouts, will next face mandatory challenger Usyk for a shot at claiming all four world titles after taking Parker's WBO 'interim' belt with the fourth defeat of his career.
"I have one thing to say: Usyk! Usyk!" Wardley told DAZN.
"I said all the way through this build-up that we picked Joseph Parker because I believe I'm at the top and I proved I'm at the top.
"All credit to Joseph Parker, he can't get enough respect from him and he deserves all the respect from the boxing community. He took a chance when he didn't have to, and we knew he wasn't going anywhere quickly. We had to pick our spots and eventually we got them out of there."
Promoter Frank Warren added: "Usyk said he wants to do it, so that's what it will be. It's a 36-minute fight and it only takes one second from him.
"I sit there in amazement for someone who had zero amateur experience, 20 fights, fighting a former world champion. Ipswich should be proud of him. That was a phonomenal performance. Edge of your seat stuff.
"Both gave everything they had. It is a story I have never seen in boxing before.
"It's really simple: Oleksandr is a great champion. His next fight will be against Fabio Wardley for the four belts. It's what he deserves for that performance."
