The Aussie, who made his name by sensationally winning the Brisbane Darts Masters as a qualifier in 2019, saw off the likes of Michael van Gerwen and newly crowned Betfred World Matchplay champion Dimitri Van den Bergh on his way to victory.
In the final, Heta rarely looked troubled and never fell behind. The pair traded the opening eight legs, with Cullen landing a match-high 154 finish, but Heta looked composed and landed a 121 checkout himself to lead 4-3.
In the tenth leg, Cullen missed inside D6 for a 126 checkout to level at 5-5, and Heta pounced, landing tops to secure the first break of throw and give himself a two-leg buffer
From there, he never looked back and sealed the victory with a stunning 120 checkout to secure his first PDC ranking title.
"I am stoked - this win today means more than anything to me. Don't get me wrong my other achievements are amazing to me, but this means ranking points towards everything else," said Heta.
"The World Series win was those top guys coming to my territory, and this is me coming into theirs and winning out of 128 of the best players.
"I thought it was a matter of time for me. I've played so well the whole time and yet might not make it past the second round - but that is what the PDC is all about.
"I may not have played some great darts today but it is all about winning, and I won those tough games and that kept me going.
In the opening game of the day Heta was forced into a last leg decider against Scott Waites, but came through to then scalp Van Gerwen in the Last 64.
Next saw the comfortable 6-1 victory over Van den Bergh, before surviving a handful of match darts in a last-leg decider with Ross Smith to sneak into the Quarter-Finals.
A comfortable 6-3 victory over Martin Schindler followed, before seeing off another former Lakeside World Champion in Stephen Bunting to book his place in the final.
For Cullen, it was his best run in a PDC ranking event since his European Tour victory last September.
He started the day with a comfortable 6-2 victory over Harald Leitinger, before seeing off Conan Whitehead 6-3 in the Last 64.
This was followed by a narrow 6-5 victory over Premier League star Daryl Gurney and a stunning 6-0 whitewash of Ricky Evans to reach the Quarter-Finals.
The 31-year-old then showed his nerve by coming through two last-leg deciders, edging out Gerwyn Price 6-5 in the Last Eight, before squeezing out Nathan Aspinall 7-6 to set up the final clash with Heta.
Elsewhere, Day One winner Peter Wright was a Last 16 casualty as he lost 6-1 to Simon Whitlock - who went on to reach the Quarter-Finals - and it was a day to forget for Rob Cross who crashed out in the Last 64 to Ross Smith.
The PDC Autumn Series continues tomorrow at the H+ Hotel in Niedernhausen, Germany, with play will commencing from 1200 local time (1100 BST).
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