The Englishman entered the final day in the desert with a one shot lead and, while he was briefly caught, he was never passed, carding a 67 to get to 19 under and finish two shots ahead of countrymen Matthew Fitzpatrick and Tommy Fleetwood, and Frenchman Victor Perez.
Fleetwood - a two time winner at this event - carded a 63 for his lowest round at Abu Dhabi Golf Club on his 29th birthday, while Perez matched him for the lowest round of his European Tour career.
Fitzpatrick was bogey free in a 67 but the day belonged to 46-year-old Westwood, who took his tally of European Tour wins to 25 - 23 years, five months and 16 days after his first - and became a winner in a fourth decade.
Westwood also becomes the eighth man to win multiple Rolex Series events, joining countrymen Fleetwood, Tyrrell Hatton, Justin Rose and Danny Willett, Swede Alex Noren, Austrian Bernd Wiesberger and four time winner Jon Rahm.
His last win at the 2018 Nedbank Golf Challenge hosted by Gary Player was his first European Tour victory in over four years, and an emotional Westwood admitted in Sun City that he had feared his days in the winner's circle may have been over.
"I can't believe I'm that old," he said, showing emotion again as it dawned on him that he had won in the 90s, 00s, 10s and 20s. "It's getting harder.
"It's just nice to come out and keep proving that you've still got it.
"I won my first tournament in 1996 in Sweden. I won that tournament in three different decades and now won here this week. The 20s could be the ones for me."
On the prospect of a potential 11th Ryder Cup appearance in the autumn, he added: "I'm not sure I can take any more Ryder Cups, I've played ten and it was good watching the lads last time. But if there's a chance of that I might as well go for it."
Fitzpatrick took advantage of the par five second, holed a long putt on the third and hit a stunning tee shot to three feet at the fourth to share top spot.
Westwood had also birdied the second before holing a long putt of his own on the third to retake the solo lead, and he would not be caught again.
After saving par from the sand on the fourth, he played an exquisite bunker shot to set up a gain on the fifth and lead by two.
Fitzpatrick got up and down from sand on the eighth for a birdie but he would then make nine pars in a row as Westwood also birdied the par five after laying up.
The leader got a stroke of luck as he just avoided the water on the par three 12th but he took full advantage, holing from the fringe to lead by three.
Birthday boy Fleetwood was making a charge through the field and he birdied the first and second before playing an excellent tee shot into the fourth, holing a 15 footer at the seventh, making the most of the eighth and turning in 30 with a birdie from ten feet at the ninth.
Perez was also making a move and a big finish made him the man to catch in the clubhouse.
The 2019 Alfred Dunhill Links Championship winner was still well back despite birdies on the first, fifth, eighth, tenth, 11th and 15th.
He played a stunning tee shot into the 17th for another gain and followed that by putting his second to 12 feet for a sensational closing eagle.
Fleetwood then put his tee shots to ten feet on the 15th and 15 feet on the 16th before hitting a wonderful second from the rough on the 17th to join Perez in the clubhouse at 17 under.
Westwood failed to get up and down on the 16th for his only bogey of the day and, while Fitzpatrick broke his par run on the last to sit just one back, two putts on the par five also handed Westwood a closing gain.
South Africa's Louis Oosthuizen finished at 15 under, a shot clear of countryman Shaun Norris and England's Ross Fisher, and two clear of Wiesberger, three time champion Martin Kaymer, Masters Tournament winner Sergio Garcia and Scotland's Scott Jamieson.