Lavigne, 20, and Whibley, 25, got engaged in Venice during the last leg of her European tour. The pair, who are both Canadian, have been dating since last summer and now live together in Santa Monica. They sparked engagement rumors as far back as last September, when Lavigne was spotted showing off a large ring to partygoers at the Spider Club in Los Angeles.
On Monday night, Lavigne was sporting a ring as she and Whibley walked out of Hollywood's Chi nightclub together.
No word yet on a wedding date.
Lavigne, whose hits include "Complicated" and "Sk8er Boi," kicks off the North American leg of her current tour on July 12 in Ontario, Canada. Her latest album, Under My Skin, has sold 2.6 million copies, according to Nielsen SoundScan.
Whibley's band just wrapped up its North American Go Chuck Yourself Tour and will play dates in Europe before returning to the U.S. to open up for Motley Crue on its Carnival of Sin Tour next month.