In August 2012, Démare won the first World Tour race of his career by prevailing in the Vattenfall Cyclassics, ahead of local favorite André Greipel and Giacomo Nizzolo.

[8] On the third stage, his team-mate and lead-out rider Geoffrey Soupe produced a final power surge to launch Démare, and the duo finished one-two in the mass sprint, with Ramon Sinkeldam of Argos–Shimano taking third place.

[11] Démare struggled for form for much of the 2015 season, only scoring one top ten finish in the spring classics with a tenth place in Omloop Het Nieuwsblad.

[11] In January 2016 Démare announced his race plans for the first half of the new season, starting his campaign on home soil at the Étoile de Bessèges and Tour Méditerranéen, followed by competing in the cobbled classics of Omloop Het Nieuwsblad, Kuurne–Brussels–Kuurne, Milan–San Remo, Gent–Wevelgem, Tour of Flanders and Paris–Roubaix, along with the stage races Paris–Nice and the Three Days of De Panne.

His victory was questioned by rival riders Matteo Tosatto and Eros Capecchi, who alleged that Démare had been assisted by a tow from a team car on the climb up the Cipressa after he crashed with 30 kilometres (19 miles) to go.

[17] In Stage 6, Démare was edged out again into a second-place finish by Marcel Kittel, who launched a perfectly timed late sprint with around 200 metres to go.

[22] He took third-place finishes on consecutive March weekends at Milan–San Remo and Gent–Wevelgem,[23][24] but it was not until June before he took another victory, winning the penultimate stage of the Tour de Suisse.

[29] He was second at the EuroEyes Cyclassics,[30] before he completed a clean sweep at the Tour Poitou-Charentes en Nouvelle-Aquitaine, winning all five stages on his way to the overall victory.

[31] Démare's first victory of the 2019 season came during the tenth stage of the Giro d'Italia, which ended on the streets of Modena, prevailing in a bunch sprint ahead of Elia Viviani.

[48] After a stage win in September's Tour de Luxembourg,[49] Démare returned to the Giro d'Italia in October, as one of the contenders for the points classification jersey.

[56] Démare took his first win of the season in April at the one-day race, La Roue Tourangelle, beating Nacer Bouhanni in a sprint finish.