Bairstow gently tapped his helmet against his head upon reaching the milestone to the delight of Root and his team mates who jubilantly roared their support in the dressing room.
The wicketkeeper's 119 helped push England to 403 on day three of the third test, their highest first innings total in Australia since January, 2011.
Bairstow said his celebration was a bit of “light-hearted, fun” in reference to the October night out where he greeted Australia opener Cameron Bancroft with a headbutt at a bar.
It took nearly a month for the incident to be revealed, however, when Australia’s fielders were heard trying to get inside the Yorkshireman’s head when he was batting during the series-opener in Brisbane.
Bancroft recalled the incident in a news conference with his captain Smith sat beside him laughing heartily following England's 10-wicket first test defeat at the Gabba.
Bairstow felt he had been “stitched up” by Australia and that the event had been blown completely out of proportion.
So he celebrated emotionally at the WACA after pulling Mitchell Marsh behind square for a single to reach his ton.
“The hundred, in many ways, was my favourite one," the 28-year-old told reporters.
"I've played in a few Ashes series so far now and to score an Ashes hundred is something you dream about as a kid.
“It was really good fun out there, I absolutely loved every single minute of it.”
Bairstow was unable to truly cash in, with his batting partners crumbling around him as England lost their last six wickets for 35 runs.
He was bowled by a full inswinger from fast bowler Mitchell Starc which clipped the inside edge and uprooted middle stump.
But his first test hundred in 18 months helped tweak the narrative of England's Ashes tour, which up to Perth had been blighted by a string of off-field incidents.
It was also a part of an England record fifth wicket stand of 237 runs with Dawid Malan, who scored a fine 140.
Anchored by 92 not out captain Steve Smith, Australia moved to 203 for three at stumps, having trimmed England's lead to 200 runs.
Bairstow felt England remained well placed in the match, despite the late batting collapse in the morning session.
"You can look at it both ways and say, look, it was a fantastic recovery from being 100 for four and we've got 400 on the board," he said.
"Or you can look at it and go, 'yeah, well, we've let the position slip.
"But at the same time ... we've got the capabilities of taking five-six wickets in a session, we've shown that previously so there's no reason why we can't now."
Ashes 2017australiaDawid MalanEnglandJonny BairstowMitchell MarshMitchell StarcPerth Teststeve smith
First Published: December 15, 2017, 6:35 PM IST