Lawrie gained some momentum heading into next month's Ryder Cup with the performance, which gave him his eighth career European Tour crown.
He finished at 16-under-par 272, four better than Brett Rumford, who also shot a 68 on the PGA Centenary Course at Gleneagles.
Sharing third place at minus-11 were Fredrik Andersson Hed (65), Maarten Lafeber (69) and Romain Wattel (72).
The Ryder Cup chances of Nicolas Colsaerts were complicated by his showing at Gleneagles. He needed a second-place finish or better to join the team, but managed only a 72 Sunday, ending in a 19th-place tie at minus-6.
European captain Jose Maria Olazabal may opt to leave him off the squad when he exercises his two captain's picks Monday.