World number one McIlroy finished third at the Singapore Open to amass a lead of more than one million euros over nearest rival Peter Hanson of Sweden and secure the European Tour Race to Dubai title with two events remaining.
Hanson is not playing until the season-ending Dubai World Championship later this month while Northern Irishman McIlroy will play in Hong Kong next week and then round off his season in the Middle East.
Last year Englishman Donald became the first player to achieve the feat while McIlroy is the youngest European number one since Scotland's Sandy Lyle in 1979, who was 21 when he won his first of three order of merit titles.
McIlroy built a huge lead in the PGA Tour money list after clinching his second major at the PGA Championship in August and then winning two of the four FedExCup playoff events the following month.
"Winning a second major already made it a fabulous season, but then to follow Luke in becoming number one in both Europe and the States is the icing on the cake after a fabulous season," the 23-year-old told reporters.
"I feel so proud and humbled to have joined so many fabulous names in Europe who have won the order of merit," added McIlroy, the second Northern Irishman to win the title after Ronan Rafferty in 1989.
McIlroy had finished second in the standings in two of the last three years after securing his playing card five years ago in what has been a whirlwind career so far.
In March, then 22, McIlroy became the second youngest player to reach the top spot in the world rankings, after 14-times major winner Tiger Woods, since they were first issued in 1986.
Both of McIlroy's major wins have come in record fashion and apart from the obvious target of more victories, he said he had a long way to go to catch eight-times European Tour number one Colin Montgomerie.
"Monty won eight orders of merit in his prime and I have only won one so far, so there is plenty of ground to make up. But to be able to go into 2013 as number one on both tours is hugely satisfying," said McIlroy.