PGA star Johnson, 29, popped the question on August 17. The two have been dating since the beginning of the 2013 PGA Tour season.
Johnson tweeted a picture of the sparkler on Gretzky's hand shortly after the proposal, saying "She said yes!"
Gretzky posted a photo of her own on Instagram the next day.
Gretzky's brother celebrated the news on Twitter.
Celebrity Breakups and divorces of 2014 [PHOTOS]