Hillier holed from 40 feet for eagle on the 15th, made birdie from a fairway bunker on the next and then holed from six feet for another eagle on the 17th in a brilliant final round of 66 at The Belfry on Sunday.
That gave the 24-year-old a winning total of 10 under par, securing the first prize of 468,000 pounds ($A892,000) and also a place in the Open Championship at Royal Liverpool later this month.
Hillier, who began the day three shots off a six-way tie for the lead, said: "I'm gobsmacked. I think it's going to take me a while to process to be honest.
"Early on in the day I was not feeling it at all. I was a little bit uncomfortable with the driver, didn't have many chances but obviously knew there were some chances coming in.
"I didn't think I would take them that well, but obviously pretty ecstatic.
"I'm not going to lie, I was definitely looking at the leaderboard and seeing my name up there and thinking about what it would be like to finish it off but it's all a bit of a blur really."
Hillier revealed he will now cancel his planned trip to play in two PGA Tour events which take place the week before and the week of the Open.
"Late change of plans but I'm not complaining," added Hillier, who missed the cut on his Open debut in 2021.
"It's going to be a pretty awesome experience playing the Open again so I can't wait."
Hillier finished two shots ahead of England's Oliver Wilson and American Gunner Wiebe, who secured the other two spots up for grabs at Hoylake.
Wilson birdied the 18th to snatch the final Open spot from Scotland's Calum Hill, who had to settle for a share of fourth place with compatriot Ewen Ferguson and pre-tournament favourite Justin Rose.
Rose was seven under par after an opening 65, but finished on the same total following subsequent rounds of 73, 74 and 69.
8°C