In August 2014, Dennis made a rare mid-season transfer to the. He went on to win the World team time trial championships with his new team. On 8 February 2015, he set a new hour record of, beating Matthias Brändle's record by over 600 metres. The record stood until 2 May 2015, when it was broken by Dowsett. Dennis was selected to ride the Tour de France as part of the squad supporting Tejay van Garderen. He won stage one's individual time trial, clocking an average speed of and became the first yellow jersey wearer of the Tour. With this performance, he established a new record average speed for an individual time trial at the Tour de France. He won the Sir Hubert Opperman medal and trophy for Australia's best all-round cyclist in 2015. He was named in the start list for the 2017 Giro d'Italia, however he abandoned the race on the 4th stage after injuries due to a crash on stage 2. Subsequently at the 2017 Vuelta a España, Dennis crossed the line first as part of the BMC squad that won the race's opening team time trial, taking the race leader's red jersey and becoming the first Australian to lead the race since Michael Matthews in 2014. At the 2018 Giro d'Italia, Dennis was narrowly defeated in the opening time trial by Tom Dumoulin. However, he took the pink jersey on the second stage by picking up a time bonus in an intermediate sprint. In doing so, he became the first Australian to lead the Giro since Simon Clarke in 2015, and the third Australian to wear the leader's jersey in all three Grand Tours, after Bradley McGee and Cadel Evans. He went on to win the stage 16 time trial and finished the race in 16th place overall, 56 minutes and 7 seconds down on winner Chris Froome. When he won the first stage at the 2018 Vuelta a España he became the 95th rider in history to have won at least one stage in all three Grand Tours, and the 15th rider to have won an individual time trial at each Grand Tour. He went on to win the stage 16 time trial, and left the Vuelta immediately after to prepare for the World Championships in Innsbruck, winning the individual time trial title by over a minute ahead of defending champion Tom Dumoulin of the Netherlands. He also helped his BMC team win the bronze medal in the team time trial event. At the end of 2018, he won two major Australian awards: Australian Institute of Sport Performance Awards – Male Athlete of the Year and Cycling Australia's Sir Hubert Opperman Medal, which he had previously won in 2015.
Bahrain–Merida (2019)
In August 2018, it was announced that Dennis would join in 2019 on a two-year deal, making the move from BMC alongside team-mates Damiano Caruso and Dylan Teuns. On 18 July 2019, he abandoned the Tour de France during Stage 12. No reason was immediately given, but later reports indicated that his abandonment was the result over frustration with equipment provided by the team. On 25 September 2019, Dennis raced for the first time since abandoning the Tour de France, winning gold in the men's individual time trial at the Road World Championships in Yorkshire. Dennis rode an unmarked BMC bicycle during the World Championship time trial, rather than his trade Merida machine. Several days later, his former team confirmed that they had parted ways with Dennis on 13 September.
Team Ineos (2020–)
On 9 December 2019, it was announced that Dennis would be joining for the 2020 season.
