[citation needed] On 19 July 2016, UCI World Tour team Quick-Step Floors announced the signing of Mas for 2017 season.

He continued his form, 2 months later when he placed 4th overall at the Tour de Suisse, and won the Young rider classification.

With his performance on stage 20, Mas moved from 4th to 2nd place overall in the Vuelta, finishing on the podium in just his second Grand Tour.

During the 2020 season he earned top 5 finishes in both the Tour and the Vuelta and won his second young rider competition in the latter.

During that Vuelta he assisted Primož Roglič in securing his second title through the circumstances of the race situation.

Mas rode in the 2021 Tour de France, which was marred by crashes and bad weather early in the race.

He lost time to Roglič on stage seventeen, which included a summit finish at Lagos de Covadonga, crossing the line with the surviving GC favorites about a minute and a half behind.

Mas was able to stay in the lead group and went into the final time trial about two and a half minutes behind Roglič, finishing in second overall.

Mas finished the season with a strong performance in the Italian autumn classics, where he defeated Tadej Pogacar to win the 2022 Giro dell'Emilia,[14] and placed second in Il Lombardia.

[15] Mas started the 2023 Tour de France but was involved in a crash on the first stage; he and Richard Carapaz had to withdraw.