The 27-year-old from Ballyconnell in Co Cavan carded a five-under-par 67 in the final round of the 54-hole competition at the Crown Colony Golf and Country Club in Florida.
Maguire, playing in her 50th LPGA tournament, finished on 18-under-par to win by three shots from Lexi Thompson.
“Hasn't really sunk in yet. It's a bit surreal. It's been a long time coming and I suppose you don't know it's going to happen until it actually does,” said Maguire.
She went into the final round tied for the lead with American Marina Alex, four strokes clear of Brittany Altomare, Stacy Lewis and Sweden's Linnea Johansson, but pulled away on the back nine with a majestic display of ball-striking.
Maguire’s win came the day before her mother’s birthday, gifting her the performance of a lifetime.
“Tried to just stay really patient today,” added Maguire. “Didn't get ahead of myself. Wanted to go out and just shoot a number.
“Didn't want anybody to have to hand it to me. I wanted to go out and win it myself and earn it. Yeah, just really proud of the way I played today.”
Heading into the final day tied for the lead with Marina Alex, Maguire said she didn’t look at leaderboards until the fairway on No. 18 and didn’t know how the results were beginning to net out.
After carding her first birdie on No. 2, Maguire picked up speed after a bogey on No. 3 with back-to-back birdies on Nos. 7 and 8 and closed with a 33 on her back-nine holes.
“I think the birdie on 7 was huge. Brittany [Altomare] had gone on that run early, and as I expected, I knew someone was going to go low today. I was just trying to keep up with her and Marina early on,” said Maguire.
“That birdie on 7 and 8 as well out of the pine straw was huge for momentum making the turn, and then another two on 10 and 11. I thought the shot on 11 was in. But, yeah, just some really solid iron shots to set up those chances.”
In her first start of the new LPGA Tour season, Scot Gemma Dryburgh finished in a tie for 59th, closing with a 72 for a three-under total.