Russell and contractor Shane Deary, both 30, became engaged last year, said Jill Fritzo, the actress' publicist. No wedding date has been set.
She portrayed spirited college student Felicity Porter in "Felicity" for four years. The series ended in 2002.
Russell has since starred in the films "Mission: Impossible III" and "The Upside of Anger," and the TV miniseries "Into the West."
Her new movie, the independent romantic comedy "Waitress," will screen at the Sundance Film Festival next week.