The 19-year-old reigning French Open champion took just 45 minutes to dispatch the 2019 Rome winner two weeks before she opens her title defence in Roland Garros.
Swiatek, ranked 15, claimed her third WTA title having followed her Roland Garros success with a win in Adelaide in January.
"I'm really, really happy," said an emotional Swiatek.
"I'm overwhelmed, at the beginning of this tournament I would not have dreamed of winning it."
Swiatek swept through the first set in just 20 minutes, with Pliskova winning just four points.
Pliskova tried to fight back in the third game of the second set, holding a double break to go 2-1, but the Polish player ruthlessly snuffed out any return.
"I will just quickly forget about today," said Pliskova, the world number nine, who was playing in her third consecutive Rome final.
The former world number one retired injured in last year's final to Romania's Simona Halep. 
"I've had some great matches here, in the past I did well."