Amateur career Dillier was born in
Baden, Switzerland. In 2008, he was the Swiss national junior time trial champion, Under-23 road champion in 2009, and Under-23 time trial champion in 2010 and 2011. In 2012, he won a stage at the
Tour de l'Avenir. This prompted BMC to sign him to a contract for the 2014 cycling season.
BMC Racing Team (2014–17) He was named in the startlist for the
2016 Vuelta a España. Dillier rode in the
2017 Giro d'Italia. and won Stage 6 in a two-man sprint against
Jasper Stuyven () after the pair had been part of a five-man breakaway that rode clear of the peloton for almost all of the stage. In June 2017, Dillier won his first stage race, the
Route du Sud.
AG2R La Mondiale (2018–20) at the
2018 Paris–Roubaix; he ultimately finished second to Sagan in a sprint finish. Dillier joined for the 2018 season to bolster the team's classics squad, but he suffered a broken thumb at
Strade Bianche. He returned to racing in April 2018 and won his comeback race,
Route Adélie. At
Paris–Roubaix, Dillier was part of a nine-man early breakaway that escaped from the peloton after an hour of racing, and was leading with
Jelle Wallays (), until the pair were caught by world champion
Peter Sagan (), who had attacked from the group of favourites with around remaining. Dillier was able to stay and work with Sagan all the way to the finish at
Roubaix Velodrome, where Sagan won the two-up sprint finish. In July 2018, he was named in the start list for the
Tour de France.
Alpecin–Fenix (2021–) In November 2020, Dillier signed a one-year contract with the team, for the 2021 season. He extended his contract by a further two seasons in July 2021. Diller became known as a reliable domestique for
Mathieu van der Poel. At
Milan-Sanremo, he would regularly ride approximately 200km, often unassisted by other teams, at the front of the peloton. ==Personal life==