Four birdies on the front nine in a round of 68 at Buckinghamshire Golf Club saw the 26-year-old South Korean end on a four-round total of 18-under-par 270, holding off the challenge of Australian Nikki Campbell, who had two eagles and a birdie in her 67.
Rising star Stephanie Meadow from Northern Ireland, playing in her second event as a professional after finishing third two weeks earlier at the US Women's Open, equalled the course record with nine birdies in a 63.
She ended in a share of third on 11-under-par, alongside South African Lee-Anne Pace and Germany's Caroline Masson.
In bright and breezy conditions, Kim collected her fifth victory as a professional and her first since the 2010 Lorena Ochoa Invitational. She said that caddie, Gerald Adams, whose nose was broken by a stray golf ball during the Pro-Am on Wednesday, had inspired her to win the event.
"It's amazing that he was caddying for me on Thursday because he got hit by a golf ball on Wednesday and was bleeding everywhere. His attitude towards living and daily life is inspiring to me and many people on the tour," said Kim. Adams recovered from prostate cancer last year.
The World No.24 continued: "I just had a great time. It's great to win the tournament and this is my first time playing the course so I'm really honoured to win the championship. I feel like I've been hitting the ball really well and putting really well so I just had to go out there and enjoy myself."
Campbell, who played with Kim for the first three rounds, commented: "I played really well but couldn't catch IK. I'm happy with second."
Meadow, who had her best ever round, added: "It's been a dream start but it's also a dream to play in this environment. US Open and here: the bigger the better! It's more fun. Being out here playing for a crowd is what I love to do."
As Meadow was heading to Final Qualifying at Southport & Ainsdale for the coming week's Ricoh Women's British Open at Royal Birkdale, Hannah Jun of the United States and Ladies European Tour rookies Amy Boulden and Sally Watson could celebrate qualifying for the major championship, as the leading three Ladies European Tour members not otherwise exempt.
It was a very good week for the Australians with not only Campbell finishing runner-up but Sarah Kemp 6th, Minjee Lee 11th and Sarah Jane Smith 14th.
Leading final scores Final Scores:
270 - I.K. Kim (KOR) 71 68 63 68
275 - Nikki Campbell (AUS) 72 68 68 67
277 - Stephanie Meadow (NIR) 73 71 70 63, Lee-Anne Pace (RSA) 70 69 70 68, Caroline Masson (GER) 68 74 66 69
278 - Amelia Lewis (USA) 68 71 68 71, Stacy Lee Bregman (RSA) 70 71 68 69, Ariya Jutanugarn (THA) 72 73 66 67, Sarah Kemp (AUS) 67 68 72 71, Vikki Laing (SCO) 69 72 69 68
279 - Amy Boulden (WAL) 69 69 72 69, Hannah Jun (USA) 71 71 70 67, Minjee Lee (AUS) 71 68 67 73
280 - Charley Hull (ENG) 70 74 68 68, Sarah-Jane Smith (AUS) 72 70 67 71, Gwladys Nocera (FRA) 69 70 71 70
281 - Sophie Giquel-bettan (FRA) 74 71 67 69
282 - Katie Burnett (USA) 70 71 72 69, Sally Watson (SCO) 67 73 69 73
283 - Karrie Webb (AUS) 73 70 70 70, Diana Luna (ITA) 69 72 72 70