The model, actress and radio host is planning a wedding to entrepreneur boyfriend George Smart after 14 months of dating.
Lisa announced the news in an interview with The Sun's Fabulous magazine, revealing her new fiance proposed just before Christmas (16) and presented her with "the most beautiful diamond ring".
"George proposed on the Saturday before Christmas and it was such a lovely surprise," she said. "I had absolutely no idea he was going to do it!
"It was just us, it was really low-key and completely unexpected. He chose the most beautiful diamond ring, which I love, and amazingly it fits me perfectly! It was such a great way to start the New Year."
Snowdon dated Clooney on and off for five years.