[7] The first part of the route went south-east through Faimes and Saint-Georges-sur-Meuse before reaching the day's first climb, the Côte des 36 Tournants, after 22 kilometres (14 miles).

The route continued north to Andenne, then east to the third climb, the Côte de Bohissau, 100 kilometres (62 miles) into the race.

The first climb of the Mur came with 87.5 kilometres (54.4 miles) to the finish line; it was followed by the day's only feed zone.

[10] The final loop of the race followed the same roads as before, east out of Huy and then south-west to the Côte d'Ereffe, climbed with 16.5 kilometres (10.3 miles) remaining.

[9] Within the town, the riders were faced with a slightly different route and a climb new to the 2015 edition of the race, the Côte de Cherave.

The top of the Côte de Cherave came with 5.5 kilometres (3.4 miles) to the finish line and was followed by a sharp right-hand turn and a fast descent back into Huy.

[11] The crucial part of the race was the final 1,300-metre (4,300 ft) climb of the Mur de Huy, with an average gradient of 9.6%.

The addition of the Côte de Cherave, however, added an unknown factor into the race: it was considered much more likely than in previous years that a group of riders could break away from the peloton on the penultimate climb and hold an advantage to the finish line.

[13][15] Other riders considered to have a chance of victory included Dan Martin (Cannondale–Garmin), Sergio Henao (Team Sky) and several other climbers and puncheurs.

[13] As the third stage of the Tour de France was scheduled to finish on exactly the same roads, several riders who were aiming at success there rode La Flèche Wallonne as preparation.

There were seven riders in the break: Thomas De Gendt (Lotto–Soudal), Mike Teunissen (LottoNL–Jumbo), Brice Feillu (Bretagne–Séché Environnement), Jérôme Baugnies (Wanty–Groupe Gobert), Reinier Honig (Team Roompot), Daniele Ratto (UnitedHealthcare), and Pieter Vanspeybrouck (Topsport Vlaanderen–Baloise).

Dan Martin, one of the favourites for the race, touched wheels with Tiago Machado (Team Katusha) and both riders crashed.

Honig and Teunissen were dropped from the leading group on the second climb of the Côte de Bellaire.

[16] The most significant rider caught in this crash was Philippe Gilbert; others were Julián Arredondo and Bob Jungels (both Trek Factory Racing).

[18][20] Another crash happened shortly afterwards, involving Jelle Vanendert (Lotto–Soudal), Alexey Tsatevich (Team Katusha) and Kévin Reza (FDJ).

[19] On the penultimate climb of the Mur, the breakaway split; only De Gendt and Baugnies remained in the lead, 50 seconds ahead of the peloton.

[16] Tejay van Garderen (BMC Racing Team) attacked on the Col d'Ereffe, while Visconti and Sánchez soon dropped De Gendt and Baugnies.

Vervaeke, Van Garderen and Baugnies combined briefly, but were unable to catch the leading pair and were themselves caught by the peloton with 13.4 kilometres (8.3 miles) remaining.

On the climb, Vincenzo Nibali attacked; he could not build a gap to the group, but did bring them closer to Visconti and Sánchez.

Giampaolo Caruso (Team Katusha) attempted to follow; he was unable to join Wellens and was recaptured by the pack soon afterwards.

[25] The 2015 race was his third victory in La Flèche Wallonne, bringing him level with Eddy Merckx; Valverde described this as a "great honour".

[32] Riders who finished in the top ten in La Flèche Wallonne were awarded points in the UCI World Tour rankings.