It's the seventh career title for Halep, with the other six all won last year.
"I think it's the best, because it's the biggest tournament which I won," Halep said.
For the first time Halep defeated three top-10 players at the same event — No. 7 Sara Errani in the quarterfinals, No. 4 Agnieszka Radwanska in the semifinals, and the ninth-ranked Kerber.
Halep, who had a first round bye, nearly lost her opening match of the tournament before defeating Kaia Kanepi in a third-set tiebreaker in the second round.
In the updated rankings, Halep will move from a current career-high 10th to ninth. Kerber will go from ninth to eighth.
Kerber was unable to break Halep's serve despite four break point opportunities in the match.
"It's tough to play against a player like Simona," Kerber said. "I was trying to play my game plan, but it was not easy ... she hit the balls very well and on the line."
Kerber dropped serve twice in the first set, including at love on a double fault in the first game.
Halep had to save two break points when serving for the set at 5-2. She ended up winning the game on Kerber's backhand error.
In the second set, Halep also broke serve twice — in the fifth and ninth games.
"I just want to be focused for every point, to fight for every point," Halep said.
To add to Kerber's dismay she double-faulted on the final point of the 66-minute match.