The 26-year-old Wiesberger made four birdies on his way to claiming the win to become only the third Austrian to win on the European Tour after Markus Brier and Martin Wiegele.
''I played the best three rounds of my life over the last few days.'' Wiesberger said. ''My game plan was to hit as many greens as possible and give myself birdie putts.
''I had bad pace early on today and left a few short, but they dropped in the end.''
''It was a fantastic day,'' Ramsay said. ''I was a bit nervous going out but I had some mental notes in my head and every time I got a little bit nervous, I went back to them.''
Victor Dubuisson, who had led after the first round, finished third alongside Australian Marcus Fraser. Another Australian, Adam Scott, the highest ranked player at the event at No. 12, finished 12th after shooting 65.
''It's a good time to be starting to play good,'' Scott said. ''There are three majors left this year, and the Players Championship amongst other things. Lots to play for.
''You can always take confidence from playing well,'' he added. ''It's nice to be able to get some birdies, hit some good shots and I'll take that stuff back with me to the States.''
Wiesberger went 55 holes without dropping a shot during the tournament, after making a double bogey on the No. 13 par-3 in his first round.
His victory gives him his European Tour playing card until the end of 2014.
Englishman Ian Poulter finished tied for 15th with a 281, as did Y.E. Yang.
Paul Casey continued to step up his comeback from a shoulder injury and finished 25th at 5 under, finishing 1 under for the day.
Spaniard Miguel Angel Jimenez managed his first top-five finish of the season after finishing 10 under.