Bangladesh put on a respectable 196-6 after being sent to bat first but Haris made a mockery with the visiting bowlers to smash 46 ball-107 not out, leading the side to victory with 14 balls to spare.
Bangladesh hinted at making it hard-fought for Pakistan, when Mehidy Hasan Miraz removed Shahidzada Farhan (1) in the first over after the batters put up a decent show for the first time in the series.
Haris showed the value of the power-hitting, something what Bangladesh batters lacked in the shortest format of the cricket.
He struck eight fours and seven towering sixes in a knock, featured with calculative risk as he never changed the attacking gear when he got his eye in.
Even after the early dismissal of Farhan, Haris continued hitting at will and got the support from Saim Ayub who also was at his attacking best.
Together they tore apart Bangladesh bowling and added 92 runs from just 53 balls. Tanzim Hasan Sakib broke through with the wicket of Saim who hammered 45 off 29, studded with two fours and four sixes.
When he was dismissed, Pakistan already put them in a position of dominance. Bangladesh needed wicket but there was no respite for them as Hasan Nawaz matched with Haris’s aggression to further send the bowlers in receiving end.
Miraz, who was the most successful bowler for Bangladesh with 2-26 in three overs, removed Nawaz after he made 26 off 13.
Haris then raised his maiden century off 45 balls, swiping down Hasan Mahmud in mid-wicket for two. He celebrated the century with a six and then captain Salman Agha who stayed not out with Haris for 15, struck a boundary and a single in consecutive deliveries of Towhid Hridoy to seal the deal in incredible ease.
Bangladesh lacked in relentless attack, the mantra of T20 cricket, despite getting a resolute start from the openers.
Opener Parvez Hossain Emon blasted a 34 ball-66 and his fellow opener Tanzid Hasan Tamim contributed 42 off 32.
They put on 110 runs in just 10.4 overs to lay a solid foundation but the middle order couldn't come all guns blazing that eventually restricted them below 200.
The partnership was broken with the dismissal of Tanzid who made 42 off 32 with three fours and as many sixes.
Emon who smashed seven fours and four sixes in his audacious knock followed Tanzid in the next over while trying to dispatch Shadab Khan with a high risk slog sweep shot.
Towhid Hridoy then made 25 and skipper Liton Das added 22 but they lacked the power-hitting skill and the knack for relentless attack, something what Haris and Saim Ayub showed in chasing.
Hasan Ali and Abbas Afridi took two wickets apiece and curbed the aggression of Bangladeshi batters in the death overs, reports BSS.
Earlier, Bangladesh lost the first match by 37 runs and the second one by 57 runs. The series whitewash came after they suffered a shock 2-1 defeat to ICC associate nation United Arab Emirates (UAE).