The FDJ-BigMat rider beat Britain's Adam Blythe (BMC) to the line in a bunch sprint at the end of the 153.8km stage from Mons to Tournai.
Lotto-Belisol's Roelandts finished third and took the GC after winning the opening stage of the four day race now known as the Tour de l'Eurometropole.
Jean-Lou Paiani, Thomas Bertolini, Tim De Troyer, Boris Dron and Gediminas Bagdonas were involved in the break of the day.
They were joined by Serge Dewortelaer and Rob Ruigh and had a maximum lead of 3:48 on the peloton.
But they were caught with 40km to go and a series of counter-attacks were foiled on the run-in to the line as former Belgian champion Roelandts won the first stage race of his career by 17 seconds from Team Sky's Juan Antonio Flecha.
Roelandts, who missed the early season after fracturing a cervical vertebra in January in Australia, was rejoiced "to have found (his) best level."
"I finished the season in the best condition when it started with a disaster. I still have a big event, the Paris-Tours on Sunday," he said.
"The Paris-Tours profile suits me and I am very motivated. I proved in the world championship that I had the legs for a route over 250km," said Roelandts.