Six days after narrowly avoiding a humiliating defeat at the hands of the Test minnows, normal service was resumed for the world's best side as they finished the third day on 364-3 in reply to Bangladesh's paltry 197.
Gillespie, normally a star with the ball rather than the bat, was unbeaten on 102 alongside Mike Hussey on 92 at tea before rain brought an early end to the day's play with the tourists 167 ahead.
Australia's opening bowler began his innings as a night-watchman near the end of Sunday's opening day after earlier starring with the ball by picking up three of the Bangladesh top order before lunch.
The paceman, who turns 31 on Wednesday and was dropped by Australia after their surprise Ashes defeat in England last summer, enjoyed his promotion up the batting order smashing 17 fours in his 300-ball knock.
He brought up his well-deserved ton in style by driving left-arm spinner Abdur Razzak for a four through the covers just before the tea break. His previous Test best was 54 not out against New Zealand at Brisbane in 2004.
"Me getting a century is bizzare. I had decided to go out there and bat for as long as possible but never thought that I could remain not out for so long or get a century," said Gillespie.
"I am naturally very, very happy to get the century because I thought the Bangladesh bowlers were not that bad," said Gillespie, who had not even had a century in first-class cricket before Tuesday's effort.
"Their young pacers were getting bounce and the spinners were pushing the ball through but I was lucky to hang around," he added.
The Australians looked keen to ensure that they did not have to bat a second time in the match, the final game in the series.
Hussey helped himself to some easy runs against a pedestrian bowling attack, hitting 14 fours off 120 balls, and putting on 154 runs for the unbroken fourth-wicket stand with Gillespie.
Gillespie played through the rain on Monday when only 22.4 overs could be bowled.
Resuming Tuesday on 28 with the team score at 151-2, he dropped anchor at one end with overnight partner Ricky Ponting hitting out confidently at the other.
Skipper Ponting, 19 overnight, scored 52 off 92 balls with four fours and a pulled six over the square-leg fence off paceman Shahadat Hossain, before he was run out.
Gillespie sent his captain back after playing the ball towards gully and a direct hit from Abdur Razzak at the bowler's end had Ponting stranded in no-man's land.
Gillespie and Ponting, who made an unbeaten 118 in the second innings to guide his team to a three-wicket win in the opening Test in Fatullah, had put on 90 for the third-wicket.