Dumoulin started his professional career in 2012 at the age of twenty-one with Argos-Shimano. In his first year as a professional cyclist, he achieved several good results in time trials and stage races.

In his second year as a professional cyclist, Dumoulin manages to find his way to the podium more often. He finished third in the Dutch Time Trial Championship. A few days later he claims the silver medal in the road race championship in Kerkrade.

In 2014 Dumoulin won his first pro races. That year, he won, among other things, the Dutch National Time Trial Championship and the time trial in the Eneco Tour. He also won the bronze medal at the World Championships Time Trial.

A year later, Dumoulin experienced his breakthrough. He wins three time trials at World Tour level and wears the red leader's jersey for several days in the Vuelta a España. Many people will especially remember the stage 9 of that Vuelta. Dumoulin came back from lost position, leaving Chris Froome behind in the last hectometre.

In his home country, Dumoulin conquers the first pink jersey of the Giro d'Italia of 2016. A month later, the Limburger takes his second national time trial title. During his fourth Tour de France, Dumoulin manages to achieve two stage victories, but in the nineteenth stage he gave up injured. A broken wrist clouds his preparation for the Olympic Games in Rio de Janeiro. Nevertheless, Dumoulin rushes to the silver medal in the time trial at the Olympics.

2017 is the year in the career of Tom Dumoulin. With two stage wins, he assures himself of the overall win in the Giro d'Italia in the final time trial in Milan. This makes him the first Dutchman since 1980 to win a Grand Tour. After the Giro d'Italia, Dumoulin once again contests the Dutch National Time Trial Championship in his favor and also wins the BinckBanck Tour. In Bergen, Norway, the then 26-year-old Dumoulin crowns himself world champion time trial.

In both the Giro and the Tour, Dumoulin wins a time trial in his rainbow jersey and in both grand tours he finishes second in the general classification. At the World Time Trial Championships, Dumoulin takes the silver behind Rohan Dennis. He finishes fourth in the road race.

In 2019 Dumoulin has a bad year. In the fourth stage of the Giro d'Italia he crashes, causing a knee injury and leaving the race the next day. Those knee problems also affect him in the Critérium du Dauphiné, which means the end of the season for him.

In the winter of 2020, Dumoulin transfers to Team Jumbo-Visma. Partly due to the corona crisis, he debuts in yellow and black in August. In the Tour de France, Dumoulin finishes seventh in the general classification.

At the beginning of 2021, Dumoulin decides to take a break from cycling to consider his future. A few months later he announces his return with the big goal: the Olympic time trial. Via the Tour de Suisse and the Dutch championships, where he conquers his fourth national time trial title, he is working towards the time trial in Tokyo. Just over a minute behind teammate Primoz Roglic, Dumoulin finishes in second place. A second silver medal at the Olympics, but this time with a better feeling than a few years ago.

In 2022, Dumoulin has an unlucky season. A back injury hampers his performance. At the beginning of June, Dumoulin announces that this year will be his last as a professional cyclist. A decision he will come back from in August: Dumoulin immediately ends his cycling career.