The Italian, ranked 21 in the world, had gone almost four years without a tour win coming into the final but needed only 75 minutes to record a superb 6-2 6-1 success at the WTA Premier hard-court event.
Pennetta had to deal with some early pressure on Sunday but soon took control against Radwanska, who was hampered by a knee injury as the match wore on.
After breaking at 2-2, Pennetta went on to close out the opening set in clinical fashion.
Radwanska won the opening game of the second but then needed a medical timeout for treatment on her left knee.
The world number three attempted to battle on but struggled to move freely and Pennetta took full advantage.
Radwanska's forehand remained solid but she could not avoid making numerous unforced errors with her speed across the court reduced.
A third break in succession sealed victory for Pennetta - and the 10th WTA title of her career.