Petersen, who lives in Bradford, became the first African player to win a Professional Darts Corporation (PDC) ranking event when he defeated Jonny Clayton 8-3 in the final of the German Darts Championship in Hildesheim.
Just 12 days after missing four darts to win his first PDC title at the Autumn Series - against Gerwyn Price, who he defeated in Saturday's second round - Petersen got over the line as the European Tour returned from a six-month absence.
The in-form 33-year-old will now look forward to a debut at the World Grand Prix and Grand Slam of Darts in October and November respectively.
"I've been working hard for what feels like a lifetime, since I was 15-years-old," said Petersen, who enjoyed a £25,000 pay-day.
"The last two to three years have felt like the hardest because of the level of players I've been competing against.
"Sometimes you just feel like you're never going to get there because the players out there are so good.
"Losing to Gerwyn Price at the Autumn Series spurred me on to win this title.
"It's an amazing feeling, just fantastic."
Petersen beat Jeffrey de Zwaan 6-3 in the first round before hitting back from 5-1 down to defeat Price 6-5.
He then edged out former world champion Rob Cross 6-5 and overcame Krzysztof Ratajski 6-3 in a quarter-final before a 7-4 defeat of Danny Noppert to book a place in the final.