The Italian claimed his first top-tier title since his triumph at the 2013 BMW PGA Championship at Wentworth by shooting a round of 66 on Sunday to finish three shots in front of England's Jordan Smith.
Manassero shot seven birdies in his final round, including one at each of the last four holes, to pick up the trophy.
Tied with Smith were South African pair Shaun Norris and Thriston Lawrence, with the latter's 63 putting the pressure on Manassero, but the Italian prevailed to win a fifth European tour title.
Manassero, who lost his tour card in 2018 before claiming two victories on the Challenge Tour last season to regain his seat at the top table, said: "This has been the best day of my life.
"It has been a crazy journey over the last couple of years, I knew I was getting on the right track but then you never know when this happens.
"Even coming down the 18th with a good score, you still have to do some more. Golf is a really difficult game but I'm so incredibly happy to be here holding this trophy right now.
"I think I played really good golf today. The guys behind were playing some really good golf and every time you look at the leaderboard there is a different name with birdies so there was always somebody chasing.
"It was difficult, I had a little bit of a tough time, 12 and 13 was kind of hard but I kind of managed to go through that and the finish was amazing."
Australian Jason Scrivener finished tied for 17th after a final-round 68 left him on 16 under for the tournament.
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