The 34-year-old Englishman took over from Northern Ireland's Rory McIlroy at the summit after shooting a four-under 68 for a 15-under tally of 273 at the European Tour's flagship event.
World number 10 Justin Rose (70), partnering countryman Donald in the final round, missed a succession of birdie chances and had to settle for a share of second place with 1999 British Open champion Paul Lawrie (66) on 277.
Ireland's Peter Lawrie (71) finished in fourth position on 280.
Donald, who retained the PGA title he won for the first time last year in a playoff with Lee Westwood, became only the third player to win the trophy in back-to-back years after Nick Faldo (1980-81) and Colin Montgomerie (1998-1999-2000).
The anticipated head-to-head "Duel in the Sun" with Rose never materialised as the latter failed to convert half a dozen birdie chances while Donald plotted his way round in typically steady fashion.
Rose smashed his club into the turf in frustration at the 15th hole after a wayward approach landed in a greenside bunker.
While his partner was bogeying that hole, Donald tapped his tummy and heaved a visible sigh of relief after knocking in a knee-trembling effort from four feet.
Rose also found a greenside bunker at the 16th and his title rival effectively sealed the first prize of 750,000 euros by sinking his putt for a birdie three from 10 feet.
