A closing five-under-par 67 gave the 20-year-old former British Boys champion a nine-under-par total and a four-stroke victory over Bolivian Sebastian MacLean, Welshman Rhys Enoch and Dutchman Daan Huizing.
Australian based New Zealander, Ben Campbell, was the best of the Australasians finishing in a tie for 6th position with a two-under-par total after rounds of 69-71-73-72.
The win is Lewis' first main amateur stroke title and the world number 3 credits his father, Bryan, for his win.
"He said a couple of years ago that I would have a good chance of winning here," said Lewis after his final round.
"It was a good shout as he has been proved right. It [the Old Course] quite suits me. Even though it is wide, you still have to hit it straight and keep it up the right side."
During the Australian season Lewis contended in the first tour downunder, playing in a number of professional and main amateur events.
At the Australian Open last December in Sydney Lewis collected the amateur medal for the championship.
The week before in the Hunter Valley he'd pushed European Tour journeyman Peter O'Malley to the wire at the NSW Open championship, eventually going out to O'Malley after the third play-off hole.
The Englishman returned to Australia in January to contest the Australian Master of the Amateurs at Royal Melbourne and featured strongly for another top-10 finish. He also finished in the top 60 in the Dubai Desert Classic in February.
In 2009 Lewis won the British Boys and English Boys amateur championships before reaching the quarter-finals of the Spanish amateur championship and was runner-up at the Welsh Open Amateur Championship in the same year.
Last year at the British Amateur Championship had Jin Jeong's, an Australian based Korean, putter not been "red-hot" during their round of 16, where Jeong pipped Lewis with a 1-up win before going on to claim the title, another championship may have fallen Lewis' way.
His biggest victory before the St Andrews Links Trophy was certainly the British Boys title in 2009, yet his win at the Carris Trophy referred to as the English Boys amateur, was just as special.
As 2011 unfolds Lewis will focus upon achieving results like his win at St Andrews. His main goal this year is to make the Great Britain & Ireland team for the Walker Cup.
"Playing the Walker Cup is a huge goal for me," says Lewis.
"At the same time I want to get myself into position to win more championships and feel what it is like to put yourself under pressure. I'm usually pretty good in those situations and it is great to get a win."
These championships also proved invaluable for Ben Campbell as he secured another top-10 finish in a main international amateur event. The world number 14 will head to the British Amateur championships, to be played at Hillside and Hesketh starting 13 June in England's north west, with poise and confidence.
"I closed out this event a little poorly," said Campbell, who was still coming off the effects of a stomach bug he contracted a fortnight ago upon arriving in Scotland
"Overall it was pleasing and I'm feeling my game is there. I'm over the sickness and played in patches some good golf. That gives you the confidence to head into the amateur knowing that you are striking the ball and putting well."
Only three Australians were among the 40 qualifiers, with Daniel Nisbet finishing in a tie for 14th position ten strokes behind Lewis at two-over-par. Matt Stieger finished at 3-over-par and in a tie for 20th, while Brett Drewett was at six-over-par and 32nd.
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