The apprentice electrician from Maitland in New South Wales won a prize package of AU$100,000 (£66,668), a book deal and the chance to work with some of Australia's foremost chefs.
"I'm over the moon and I'm very proud of myself really, because I bet you anyone at the start of the competition wouldn't have picked me to win," Allen said following his victory. "Anyone about two weeks ago wouldn't have picked me to win."
Legal secretary Julia Taylor, who hails from Brisbane, finished in second place.
In addition to an AU$15,000 cash prize (£10,000), she was also given an apprenticeship by patissier Adriano Zumbo.
Audra Morrice was eliminated after the first challenge on Wednesday night's (July 25) final and finished third, taking home AU$5000 (£3,334).
MasterChef Australia also enjoyed ratings success on Wednesday, scoring 2.191 million viewers for the winners' announcement and 1.888 million viewers for the challenges according to NineMSN.
The Australia's Got Talent final attracted 998,000 viewers.
MasterChef Australia airs on Channel Ten, with a special all-stars edition of the programme scheduled during the Olympics.