Root flicked Australia paceman Scott Boland for four down the leg-side to complete his 40th test ton in 181 balls, triggering a huge cheer from the England fans at the Gabba.
The 34-year-old's previous high score from his 16 Ashes tests in Australia was 89 coming into Brisbane.
Root's hundred helped dig England out of early trouble when they were five for two in the third over in the pink-ball test at the Gabba after two Mitchell Starc wickets.
