Campbell, who won the U.S. Open earlier this year, became the fourth player to win both events in the same year, joining Gary Player, Hale Irwin and Ernie Els.
The match was tight throughout, but it was a pair of late errors by McGinley that were the turning point. Campbell's bogey on the 31st squared the match, but McGinley lost back-to-back holes from the 33rd.
McGinley, the 11th seed, chipped his third at the par-4 15th 7 feet from the cup. Campbell, who also missed the green, pitched to tap-in range and was conceded par.
The Irishman missed his 7-footer and fell 1-down. Campbell found a fairway bunker off the tee at the next. McGinley pulled his drive further left into the trees.
McGinley punched out of the trees, then knocked his third just off the putting surface. Campbell, meanwhile, found the green with his approach. He two-putted for par to take a 2-up lead with two holes to play on the West Course at the Wentworth Club.
Campbell, who defeated Geoff Ogilvy, Steve Elkington and Retief Goosen to reach the finals, found the fairway off the 17th tee. McGinley did the same, but his second came up short and left of the green in some thick rough.
The New Zealander knocked his second within 15 yards of the green and in the fairway. McGinley chipped on, but had some 20 feet for birdie.
Campbell rendered that putt useless. He pitched to tap-in range and was conceded the birdie and the match.
McGinley, who beat Angel Cabrera, Thomas Bjorn and Luke Donald to reach the final match, played the final 17 holes in 1-over par.