Dumoulin missed the first half of the 2021 season after he took an indefinite break from cycling for personal reasons, ultimately making his return to the sport at the Tour de Suisse in June and winning his fourth Dutch National Time Trial Championships later that month.

Dumoulin was born in Maastricht, and grew up in the city near the Maas Boulevard, which used to host the finish of the Amstel Gold Race.

Originally his ambition was to study medicine and become a doctor, but after not being offered a place at medical school he began a Health Sciences degree.

[9] Later that month he won bronze in the UCI World Time Trial Championships, placing third behind Bradley Wiggins and Tony Martin in Ponferrada, Spain.

[10] His second victory of the year came at the Tour de Suisse, where he won the prologue with a two-second advantage over Fabian Cancellara.

[12] In the Tour de France, Dumoulin was one of the favourites to take victory in the opening time trial on home soil in Utrecht, the Netherlands, but ultimately finished fourth.

Dumoulin eventually took a solo win in the stage, two seconds ahead of Chris Froome (Team Sky) and took back the red jersey as Chaves lost significant time.

Froome had originally been dropped, but rode at a steady tempo and came close to winning the stage before Dumoulin outsprinted him in the final hundred metres.

[22] He was named in the start list for the Giro d'Italia,[23] where he won the opening time trial on home soil in Apeldoorn, the Netherlands, to take the maglia rosa.

He won stage 9 after attacking from a breakaway on the lower slopes of Arcalis in Andorra, and riding up the climb solo in torrential rain.

[27] Dumoulin also won stage 13, a 37.5-kilometre (23.3-mile) time trial over hilly terrain in windy conditions, by a margin of over a minute to Chris Froome in second place.

[28] Despite a broken wrist, he won the silver medal in the time trial at the 2016 Olympic Games in Rio de Janeiro, behind Fabian Cancellara.

Dumoulin then won stage 10, a 39.8-kilometre (24.7-mile) individual time trial (ITT) from Foligno to Montefalco, to take the overall race lead by 2 minutes and 23 seconds over Quintana.

[31] Dumoulin won Stage 14, which featured a mountain top finish at Santuario di Oropa to extend his lead over Quintana by a further 14 seconds.

Dumoulin defended his lead until the stage 19 mountain finish in Piancavallo, where he crossed the line over a minute behind Quintana, the new race leader.

Yates won stage 9 after accelerating away with 100 metres (330 feet) to go on the summit finish to Gran Sasso d'Italia, extending his lead over Dumoulin.

[47] On stage 18 to Prato Nevoso Yates appeared to crack on the final slopes of the summit finish and lost 28 seconds to Dumoulin and Froome.

Yates cracked on the lower slopes of the Finestre, putting Dumoulin in the virtual race lead, before Froome launched a solo attack further up the climb with 80 kilometres (50 miles) left of the stage.

Froome's advantage grew throughout the second half of the stage, as Dumoulin gave chase in a group also containing Thibaut Pinot and Sébastien Reichenbach of Groupama–FDJ, Miguel Ángel López of Astana and Richard Carapaz of Movistar Team.

Froome eventually took the stage victory by more than three minutes and thereby also taking the overall race lead, 40 seconds ahead of Dumoulin, who was attacked by the other riders on the final climb after having set the pace for much of the chase.

[52][53] On Stage 11 in the Alps, Dumoulin launched an attack on a descent with teammate Søren Kragh Andersen before pressing on alone on the final steep finishing climb to La Rosière.

[63] In May it was announced that he intended to return to racing in June at the Tour de Suisse to start his preparation for the COVID-19 pandemic-delayed 2020 Summer Olympics.