From there on the fatigued Czech, whose semi-final win over Simona Halep finished after 1 am local time earlier on Saturday due to rain delays, put up little resistance.
Barty pumped her fists when Pliskova sent a forehand long on match point to hand the 22-year-old the biggest win of her career, which includes a $1.3 million pay check.
Barty said the key to the match was extending rallies on the warm day in Southern Florida.
"It was important for me to try to make it physical," Barty, the first Australian to win the Miami Open singles title, said in an on-court interview.
"Kaja has the ability to really hit you off the court and take it away from you so I knew I had to have my running shoes on today to try and make as many balls as possible."
Barty fired 15 aces, with Pliskova barely making an effort to return some of them.
"I tried to make the most of it," she said of playing an exhausted opponent.
"You don't get these opportunities every single day and it was important for me to continue and try to do the right things and enjoy the moment as well."
Pliskova, who will rise to world number four on Monday, praised her conqueror.
"I'll make it quick because I'm very tired and it was a long two weeks," the 27-year-old said.
"Congrats to Ashleigh. She played incredible all week, all the matches were close and especially today I thought she came up with some good tennis."
The win capped a memorable week for the 2011 junior Wimbledon champion, who took a break from tennis in 2014 to play professional cricket for the Brisbane Heat.
Barty, the 2018 U.S. Open women's doubles champion, is the first Australian women since Samantha Stosur to crack the WTA's singles top 10.
(Reporting by Rory Carroll, editing by Pritha Sarkar)
