Jabeur, the first Arab woman in the top 10, won 7-5, 0-6, 6-3 for her second career title.
She was playing in her sixth career final and first since a runner-up finish in Charleston last month.
Pegula, a one-time tour winner, will reach a career-high No. 11 ranking on Monday.
Jabeur improved to 3-2 in head-to-head meetings against Pegula.
The Associated Press contributed to this report.