Starting the day holding a five-shot lead, Westwood carded four birdies and one bogey at Royale Jakarta Golf Club to finish on 19 under par, comfortably clear of Jaidee.
The Thai shot a superb 65 to finish at 16 under while Marcus Both, Siddikur, Park Hyun-bin and Thithphun Chuayprakong tied for third on 13 under.
The victory means Westwood will regain the World Number One spot if Luke Donald fails to hold onto his one shot lead at the Heritage on the US PGA Tour later.
Westwood was relaxed over his possible return to top spot.
"It was about coming here this week and trying to win the Indonesian Masters and I've done that," he said.
"I've ticked every box this week so we will have to wait and see what happens."
Westwood was even par for the day at the turn before a birdie at the 11th saw him gain some forward momentum.
"Yeah, that was probably the hardest putt I had all day," he said.
"It was 15 feet and had a three feet break on it. I birdied the next with two good shots and played solidly. I managed to pick up a few shots and birdied the 16th from four feet. I was quite comfortable after that."
Jaidee has been plagued by a back injury of late but the Thai feels his 65, that featured seven birdies, shows he is nearing his best.
"It was a good round from me and I'm happy with how I played. I played my own game and focused hole by hole and shot by shot. I played very solidly," he said.
"I started very well with five birdies in the first nine and knew it would be a good day with my putter. I missed a couple of shots in the back nine which was disappointing. I feel that I'm getting back into form after my back injury."