Westwood shot a course-record 8-under 64 in the final round at the Earth Course to finish at 23-under 265.
He earned $1.25 million with the 31st victory of his career to overtake Rory McIlroy on the season-long money list and win the European Tour's first Race to Dubai since it changed from the European Order of Merit.
Ross McGowan of England was second after a 68, and McIlroy, of Northern Ireland, shot a 67 to finish third on 273.
The 36-year-old Westwood's $1.5 million bonus for finishing atop the money list took his total European Tour earnings to $6,376,984. McIlroy was next with $5,432,358.
Westwood, who won the European Order of Merit in 2000, couldn't hold back tears after finishing his round.
"This is definitely the biggest moment of my career today," he said. "Rory is only 20 - I can't 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 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 lost touch with Westwood when he bogeyed his first hole. However, a run of five birdies from the 12th ensured he would finish second. McGowan is in his second season on the tour and only recorded his first win at the Madrid Masters in October.
McIlroy, who had a lead of $120,000 in the Race to Dubai at the beginning of the week, made eight straight pars to kill any chance he had of making a run at Westwood.
McIlroy's frustration boiled over at the seventh, when he smashed a club through a wooden advertising billboard after mishitting an approach out of wood chippings lining the fairway.
However, he then produced a run of six birdies in nine holes.
Geoff Ogilvy of Australia (67) and Padraig Harrington of Ireland (68) finished tied for fourth at 274.
