Westwood shot a course-record 8-under 64 in the final round at the Earth Course to total 23-under 265 and finish well clear of Ross McGowan of England (68). Rory McIlroy of Northern Ireland (67) finished third on 273.
With the 31st victory of his career, Westwood won $1.25 million to overtake McIlroy on the season-long money list and win the European Tour's first Race to Dubai since changing from the European Order of Merit.
The 36-year-old Westwood's $1.5 million bonus for finishing top of the money list took his total earnings to $6,376,984. McIlroy was next with $5,432,358.
Westwood, who won the European Order of Merit in 2000, was reduced to tears soon after finishing his round.
"This is definitely the biggest moment of my career today," he said. "Rory is only 20 - I cant even remember what it was like to be 20 - and he will have many more chances ahead of him to win the money list. "But this is my moment."
Westwood led by two shots entering the final round and opened it with five birdies in his first seven holes. He later revealed his caddy Billy Foster had given him some advice at the beginning of the week in Dubai.
"Billy told me to go out and bully other people. To make them take notice of me, rather than the other way round," Westwood said.
McGowan, in only his second season on tour and who recorded his first win at the Madrid Masters in October, lost touch with Westwood when he bogeyed his first hole. However, a run of five birdies from the 12th ensured he would finish second.
McIlroy, who had a lead of $120,000 in the Race to Dubai at the beginning of the week, made eight straight pars to stop any chance of making a run at Westwood.
McIlroy's frustration boiled over at the seventh, smashing his club through a wooden advertising hoarding after mishitting an approach shot out of wood chippings lining the fairway. He could face disciplinary action from the European Tour.
However, he then produced a run of six birdies in nine holes.
Geoff Ogilvy of Australia (67) and Padraig Harrington of Ireland (68) finished joint fourth on 274.