Applegate's publicist, Ame Van Iden, said Friday that the couple of two years became betrothed on Valentine's Day.
This will be the second marriage for both the actress and the Dutch rocker. No wedding date has been set.
Applegate's recent credits include TV's "Samantha Who?" and the movie "Alvin and the Chipmunks: The Squeakquel." She is set to appear with Drew Barrymore and Justin Long in the film "Going the Distance," due this summer.
Lenoble is a founding member of the rock group Porno for Pyros.