Macpherson, who just completed his sophomore year with the Bulldogs, becomes only the second Australian to win the British Amateur.
"I can't believe it just yet. It feel's pretty good to bridge the gap of 57 years. I hope there are a few proud Aussies having a barbecue," he said.
Macpherson went one down after the first hole, but after winning the sixth and ninth holes, he established a lead that would last.
Earlier this month, Macpherson defeated Augusta State's Olle Bengtsson 6 and 4 in the final of the NCAA Championship in Stillwater, Okla. The Bulldogs fell to the Jaguars, however.
EUROPEAN TOUR: In Saint-Omer, France, Matthew Zions, of Australia, shot 4-under 67 to build a three-stroke lead after the third round of the Saint-Omer Open.
Zions had consecutive birdies on the last two holes for a 6-under 207 total.
George Coetzee, who led after the first round, shot 72 and shares second place with Daniel Denison (67) and Federico Colombo (71).
Former Augusta State golfer Jamie Elson shot 71 and is tied for 15th at 214.
NATIONWIDE TOUR: In Wichita, Kan., Australian Matthew Goggin shot 5-under-par 66 and takes a one-stroke lead into the final round of the Wichita Open.
Goggin is at 16-under 197 at Crestview Country Club.
Kyle Thompson and Troy Kelly each had 67s and are tied for second.
North Augusta native Scott Brown shot 66 and is three shots back in fourth.