World number five Pegula quickly built a 3-0 lead in the first set as she kept Ukrainian Svitolina near the baseline before getting the first break with a backhand cross-court shot and holding her own serve with a masterful backhand slice.
Svitolina's attempt to bounce back ended when former US Open finalist Pegula saved two break points to go 5-1 up. A frustrated Svitolina netted a forehand as Pegula took the set.
American Pegula, who turns 32 on Tuesday, was measured in the second set as she got a decisive break in the fifth game to secure her 10th title on the tour, ending a three-match losing streak in WTA 1000 finals.