[6] Vanmarcke moved to Topsport Vlaanderen–Mercator midway through the 2009 season,[7] recording top-ten finishes at the Sparkassen Giro Bochum – eighth on his début with the team[7] – and the Kampioenschap van Vlaanderen (sixth).

[10][11] Also in the first half of the year, Vanmarcke recorded further top-ten finishes at Dwars door Vlaanderen (seventh),[12] E3 Harelbeke (fifth),[13] and the Rogaland GP (third).

In the first part of 2013, Vanmarcke put his focus on the Classics, but he injured his knee in a crash at Tirreno–Adriatico, which effected his preparation for the first important one-day races of the season.

[40] Over the following two weekends, Vanmarcke finished third at the Tour of Flanders – being beaten by Sagan and Cancellara, after suffering from cramps on the Paterberg[41] – and fourth at Paris–Roubaix,[42] having featured in the race-defining breaks at both races.

Having started his 2017 season in Iberia with appearances at the Volta a la Comunitat Valenciana – where he crashed twice[46] – and the Volta ao Algarve, Vanmarcke finished third at Omloop Het Nieuwsblad,[46] losing out in a sprint finish against Greg Van Avermaet and Peter Sagan, having forced the lead move on the final ascent of the Molenberg climb.

[46] Just as was the case in 2017, Vanmarcke's first podium of the 2018 season came with a third-place finish at Omloop Het Nieuwsblad; he had been part of a small group in the closing kilometres, unsuccessfully tried to chase down the race-winning solo attack by Michael Valgren, and was out-sprinted for second place by Łukasz Wiśniowski.

[51] These results led Vanmarcke to believe that he was a contender for the Tour of Flanders,[51] to be held the following weekend; however, he finished outside the top ten due to several crashes and a puncture.

[53] Over the remainder of the season, Vanmarcke took only one further top-five result, with a fifth-place finish coming at the Belgian National Road Race Championships in June.

[54] Vanmarcke started the 2019 season with a block of racing in France, finishing fifth overall at the Étoile de Bessèges,[55] before winning the opening stage of the Tour du Haut Var, recording his first victory since 2016.

[56][57] Vanmarcke's best result from the spring classics was a fourth-place finish at Paris–Roubaix,[58] and he did not reach the podium again until his victory at September's Bretagne Classic Ouest-France, where he was part of a lead group – along with Tiesj Benoot and Jack Haig – that formed with 21 kilometres (13 miles) remaining, before Vanmarcke made a solo attack in the final kilometre for his first UCI World Tour victory.