The former world number two, making only his third appearance on the European Senior Tour, had led by three strokes going into the final round and closed with a two-under-par 70, including an eagle at the fifth, to finish on 10-under with 206.
The 50-year-old, who captained Europe to victory in the 2010 Ryder Cup, finished ahead of Britain's Paul Wesselingh and Spain's Miguel Angel Martin (212) as he notched his first professional tournament win since the 2007 European Open.
"It feels great," Montgomerie said on the tour's website. "Anybody with any competitive blood in them knows that it is nice to win, to come out on top.
"This course has suited me down to the ground for years. I had a couple of great finishes on the main Tour - the Junior Tour, as I now call it - so it's nice to come back here and finally win."
Montgomerie won a record eight order-of-merit titles on the European Tour between 1993 and 2005 but failed to win a major title in an otherwise glittering career.
- Sports & Recreation
- Paul Wesselingh