Colbrelli prevailed in a sprint finish after a wet and muddy race.
Atrocious conditions saw numerous crashes, with riders struggling to stay upright, particularly on the notorious cobbled sections, and covered from head to foot in mud.
Colbrelli, Lotto Soudal’s Florian Vermeersch and Mathieu van der Poel of Alpecin-Fenix came into the Roubaix velodrome together and contested a sprint finish having overtaken long-time leader Gianni Moscon in the closing stages.
Bahrain Victorious rider Colbrelli was hugely emotional at the finish, holding his bike aloft in triumph before lying on the grass in tears.
Moscon held on to finish fourth, 44 seconds back, ahead of a group containing Belgisk star Wout Van Aert.