2018 saw the Dutchman attack both the Giro and the Tour. A strong field in the Giro meant that Dumoulin was unable to retain his title, eventually missing the top spot by 40 seconds. Whilst the race lead was held by Simon Yates for the majority of the race, Chris Froome was the eventual victor, with Tom finishing on the second step of the podium.
A repeat of the Giro occurred in the Tour, with him finishing second overall behind another Team Sky rider, Geraint Thomas. His tour was hampered by several mechanical incidents and a 20 second fine for drafting. Alongside a second position, another stage win adding to his tally of nine.
2019 was marred by a knee injury that meant he had to pull out of that years Giro and subsequent Tour. In August 2019, it was announced that Dumoulin would join Team Jumbo-Visma on a three-year contract.