[14] In May 2014, and having finished second to Kristof Vandewalle in the Belgian National Time Trial Championships,[15] Wellens made his Grand Tour début at the Giro d'Italia.

[16] After another second-place finish in the general classification, to Philippe Gilbert, at June's Ster ZLM Toer,[16] Wellens took his first professional victories at the Eneco Tour in August.

On the sixth stage, Wellens attacked with around 10 kilometres (6.2 miles) remaining and ultimately soloed to the win in Aywaille, almost a minute clear of his nearest rival.

The main group was not able to chase Wellens down and his lead extended during the downhill run into Houffalize; he won the stage by 49 seconds ahead of Greg Van Avermaet, with Simon Geschke third.

[26] The following month, Wellens won his first one-day race as a professional, winning the Grand Prix Cycliste de Montréal in a sprint against Adam Yates, after the duo broke clear of the field in the closing stages.

[28] The trio worked together on the descent, as Porte and Contador were chasing the general classification victory, but Wellens ultimately won the sprint on the Promenade des Anglais.

[40] At Strade Bianche, Wellens was one of four riders that went clear of the field with around 25 kilometres (16 miles) remaining, but was ultimately beaten to the finish in Siena by Michał Kwiatkowski and Greg Van Avermaet.

[41] Wellens abandoned the Tour de France during stage 15, because of heat and pollen allergies which he refused to treat with a therapeutic use exemption (TUE), which he does not approve to use.

[48] At the Vuelta a Andalucía, Wellens won stage 4 and took the lead of the overall standings, by beating Mikel Landa on the cobbled climb of Alcalá de los Gazules.

[51] At Brabantse Pijl, Wellens attacked with around 8 kilometres (5.0 miles) remaining before the finish in Overijse, ultimately soloing to victory by nine seconds over a group of six riders.

[64][65] After this, he recorded third-place finishes at Omloop Het Nieuwsblad in March,[66] Brabantse Pijl in April,[67] and June's Tour of Belgium, where he also won the individual time trial on stage three.

[86] He then won the second stage of the Tour des Alpes-Maritimes et du Var, beating Nairo Quintana to the line in La Turbie to take the leader's jersey.

[88] Before the end of the spring, Wellens had also recorded top-ten finishes at Strade Bianche (eighth),[89] and Brabantse Pijl (ninth), having been relegated from the podium of the latter due to an irregular sprint.

[92] Wellens started his season with a block of racing in Spain, recording his first podium finish with the team: a third-place result at the Clásica Jaén Paraíso Interior in February.

[93] The following week, he took his first win, taking the third stage of the Vuelta a Andalucía – which finished at Alcalá de los Gazules, on a cobbled climb where Wellens had previously won in 2018 and 2019.

[93] He was part of the lead group at Kuurne–Brussels–Kuurne, finishing in fifth position, before his season was impacted by injuries suffered in a mass crash at the Tour of Flanders, breaking his collarbone in four places.