Ryu dropped two shots on the back nine but four birdies from the South Korean's opening nine holes helped her to a final-round 69 and a two-stroke victory at 23 under ahead of compatriot Choi Na-yeon in London, Ontario.
Choi carded a five-under-par 67 to earn second spot, while fellow Korean Park Inbee completed the top three following her 68 at the London Hunt and Country Club.
Heading into the fourth round with a four-stroke advantage, Ryu opened her day with back-to-back birdies at the third and fourth holes.
The 24-year-old added a further two birdies at the seventh and ninth, before bogeying at the 10th.
She bogeyed again at the 15th as her lead evaporated to just one shot after Choi holed for birdied.
But Ryu composed herself with a birdie at the par-five 16th to restore a two-stroke cushion, which was enough to win her first title since 2012 - when she took out the Jamie Farr Toledo Classic.
"I thought, 'Everybody's nervous and Na-yeon's nervous, definitely," Ryu said.
"So I just accepted my nervousness so I just tried to enjoy it. And I hit a great shot."
Spain's Azahara Munoz (71) was six shots off the pace, having started the day tied for second.
American pair Kim Kaufman (66) and Danielle Kang (69) closed the tournament in a share of fifth position at 15 under overall.
Suzann Pettersen (68), Cristie Kerr (70), Brittany Lincicome (71) and Anna Nordqvist (72) were all 10 shots adrift of Ryu.