'I am proud of myself for playing some very good golf,' said Rumford. 'I just want to enjoy this week as I have waited so long for it.'
Ben Mason was Rumford's closest challenger at 10-under-par 274. He carded a final-round 69 to finish alone in second, four strokes ahead of Federico Bisazza.
Rumford held a three-shot lead heading into the final round and tallied his first birdie of the day at the par- third on the Val Course at Aa Saint Omer Golf Club. His lead dropped to one stroke, however, after a hot start by Mason.
Mason birdied three of his first five holes to quickly move to 11-under. The Englishman's charge was short-lived, however, and a bogey at the eighth halted his progress.
'Ben came at me early and he holed some good putts,' said Rumford. 'Not much was happening from my side so I had to dig deep and stay in the present and play the golf I had been playing all week.'
Rumford kept plugging along with a birdie at the seventh but almost gave the tournament away with an errant drive at the ninth that nearly went out of bounds. The 25-year-old ultimately managed to save par to keep his lead intact.
'I was extremely lucky but they are the breaks you need if you are to win golf tournaments,' said Rumford. 'Fortunately it went my way this week.'
He then birdied the 10th and ran off a pair of birdies starting at the 12th to open a six-shot lead over the field.
With the tournament in hand, Rumford coasted down the stretch but tripped slightly with a bogey at the 17th. Despite the late blemish on his card, the Australian walked away with his first European Tour victory and playing privileges through 2004.
After his hot start and the bogey at the eighth, Mason failed to make a move throughout the remainder of his round. He closed with 10 consecutive pars for his best career finish on the European Tour.
'I made a good start, put a bit of pressure on Brett but he responded very well,' Mason said. 'This continues the learning curve. Last group on the final day is always nice and hopefully many more to come.'
James Hepworth shot a 4-under 67 to finish at 5-under-par 279. He was joined by Damien McGrane, Mattias Eliasson and Peter Hanson in a tie for fourth.
Stuart Little, Alvaro Salto, Garry Houston, Cesar Monasterio and Martin Lemesurier were one shot further back at 4-under-par 280.
Sebastien Branger had the best finish of the French contingency. He shared 13th place with Bjorn Pettersson and Martin Erlandsson at 3-under-par 281.
Australian Brett Rumford fired a 4-under-par 67 in Sunday's final round to complete his wire-to-wire victory at the Aa St. Omer Open in northern France.
Rumford finished the tournament at 15-under par, five strokes clear of his nearest competitor, for his first European Tour title. His course-record 64 on Thursday set the tone for the week.
England's Ben Mason, who had cut Rumford lead to a single stroke early in the round, carded a 2-under 69 to close out the tournament alone in second place.
Federico Bisazza (70) of Italy came in third at 6-under par, a full nine shots behind the champion.
Peter Hanson, James Hepworth, Damien McGrane and Mattias Eliasson finished in a tie for fourth at 5-under par.