Mäder turned fully professional in 2019, with UCI WorldTeamTeam Dimension Data.[12] In October 2020, he was named a starter for the 2020 Vuelta a España.[13] He achieved a second place in the penultimate stage of the Vuelta behind David Gaudu and in the final standing he placed 20th.[9] In early 2021, he joined Bahrain Victorious.[9]
On stage 7 of the 2021 Paris–Nice, Mäder was part of the breakaway, and nearly won the stage.[14] However, in the final 50 metres, he was caught and outsprinted by Primož Roglič.[14] Mäder was given the combativity award for the day.[14] For the Giro d'Italia in 2021, he was made an assistant to Mikel Landa who eventually quit early due to injury during stage 5.[9] The next day, Mäder won the stage and dedicated his victory to the injured Mikel Landa.[9] Mäder eventually had to abandon the Giro due to an injury on his left arm.[9]
Later in the year, Mäder rode the 2021 Vuelta a España. After losing three minutes over the first eight stages, he began to perform strongly starting on stage nine, when he finished seventh on the mountain stage to Alto de Velefique.[15] Over the rest of the race, he continued his strong performance while serving as a domestique for Jack Haig. On stage 17, which finished atop the Lagos de Covadonga, Mäder finished with the elite group that finished a minute and a half down on the race leader, Primož Roglič. The result lifted him inside the top ten on GC.[16] The next day, on the race's queen stage to Altu d'El Gamoniteiru [es], Haig and Mäder finished fifth and seventh, respectively, at almost a minute down, with Mäder moving up to eighth on GC.[17] On the race's penultimate stage, Mäder and Haig, together with Roglič, Enric Mas, and Adam Yates, comprised a five-man group that escaped from the GC group on the third to last climb. The group continued to build their advantage over the other contenders, with the move allowing Mäder to rise inside the top five overall and Haig to move into the third spot on GC. Mäder also took the lead in the young rider classification as he overtook Egan Bernal.[18] He held his position in the final day time trial to finish the Vuelta in fifth and confirming his victory in the young rider classification.[19]
Charity
During the 2021 Vuelta a España, Mäder raised 10 Euros for every rider he beat in the general classification, with additional Euros for every cyclist he beat at the end of each stage.[20] He eventually raised over 4000€ for the Amsterdam-based NGO Just Diggit which focuses on re-greening deserted areas in Africa.[20] In 2022, he pledged he would continue to raise money for environmental means donating 1 Euro for every rider he beat at each stage throughout the year.[21]
Accident and death
During stage 5 of the Tour de Suisse on 15 June 2023, Mäder fell on a turn when descending from the stage's highest point at Albula Pass towards La Punt.[8] The American cyclist Magnus Sheffield had fallen at almost the exact same spot a few minutes earlier.[22] Mäder was found to be unconscious and submerged in water.[23] After being resuscitated he was airlifted by a Rega helicopter to the Kantonsspital Graubünden [de] in Chur. Mäder died from his injuries a day later, at the age of 26.[4] Stage 6 of the Tour de Suisse was cancelled, but a 20 km tribute ride to the planned stage finish took place[24] between Türlersee and Oberwil-Lieli.[25]