The reality star - who fronted the fourth season of the ABC romance reality show - confirmed on her Twitter account that she is planning to marry boyfriend Stephen Stagliano.
"Thanks so much for all the well wishes everyone!! We are super excited & can't wait to start planning our wedding, (sic)" she wrote.
"I am truly touched by every1's kind words!! I wish I had more time to reply to you all! I'm flipping through bridal magazines as we speak!!"
She added that Stagliano had proposed to her over Memorial Day weekend and it had been "hard" to keep it a secret, but they wanted to enjoy the news with their families first.
Stagliano's twin brother Michael - who appeared on Jillian Harris's season of The Bachelorette - also announced his engagement yesterday, to former Bachelor: London Calling contestant Holly Durst.
Pappas was previously engaged to snowboarder Jesse Csincsak, who she chose on The Bachelorette season finale, although they split in November 2008. Csincsak announced earlier this week that he had become engaged to former Bachelor contestant Ann Lueders.