It’s the first major and sixth career LPGA Tour victory for the 24-year-old South Korean star, who came into the tournament ranked fifth in the world.
Choi shot 1-over-par 73 on Sunday and finished at 7-under for a four-stroke victory.
Fellow South Korean player Amy Yang had 71 to finish second.
Choi came into Sunday with a six-stroke lead after shooting 7-under 65 on Saturday. She got into trouble when she triple-bogeyed No. 10, but recovered to win at the same course where Se Ri Pak won South Korea’s first major title in 1998.
“And 14 years later I’m here right now, and I made it,” Choi said. “My dreams come true. It’s an amazing day today, and like I really appreciate what Se Ri did and all the Korean players, they did. It’s really no way I can be here without them.”
Choi becomes the fourth South Korea player to win the event in five years, following Inbee Park (2008), Eun-Hee Ji (2009) and So Yeon Ryu (2011).
Choi and Yang were the only players to finish the tournament under par.
Michelle Wie finished the tournament 10-over. After shooting 66 on Friday to close with a stroke of the lead, she had weekend rounds of 78 and 80.
Top-ranked Yani Tseng finished 14-over, and still needs an Open victory to complete a career Grand Slam.
CHAMPIONS TOUR: In Pebble Beach, Calif., Kirk Triplett won the First Tee Open at Pebble Beach for his first Champions Tour title, making an early eagle and closing with 6-under-par 66 for a two-stroke victory.
Triplett, the two-time PGA Tour winner making his eighth start on the senior tour after turning 50 in March, finished at 10-under 206.
Mark McNulty was second after 69. Brad Bryant, Jay Haas and Bill Glasson tied for third at 6-under. Haas and Glasson shot 69, and Bryant had 74.
Tom Kite closed with 76 to tie for ninth at 4-under. Jeff Sluman, the 2008, 2009 and 2011 winner, also was 4-under after 67.
EUROPEAN TOUR: In Saint-Quentin-En-Yvelines, France, Marcel Siem had the perfect answer for all of his critics: a second European Tour title.
The 120th-ranked German shot 4-under-par 67 to finish at 8-under 276 and win the French Open, edging Francesco Molinari, of Italy, by one stroke.
Former Augusta State player Scott Jamieson closed with 71 and tied for 28th at 286.
Siem had five birdies and one bogey to finish at 8-under 276, earning his first European Tour title since he won the 2004 Dunhill Championship in South Africa.
He had a share of the lead in the final round of the BMW International Open two weeks ago in Germany. But he dropped five shots in three holes to slip down the leaderboard and finish sixth.
Molinari started the round in 22nd place, six strokes off the lead. He dropped two shots at his opening hole but then sank nine birdies to shoot 64 for the lowest round of the day.