The pair were photographed this week together in Rome, where Cruise on Friday will receive a lifetime achievement award at the Italian equivalent of the Academy Awards, the David di Donatello Awards.
Holmes' public relations firm — Baker Winokur Ryder — confirmed the two were dating.
Both actors have had high-profile relationships.
Cruise's first two marriages, to actresses Mimi Rogers and Nicole Kidman (search), ended in divorce. He was dating actress Penelope Cruz until the pair split last year.
Holmes and actor Chris Klein recently called off their engagement after dating five years.
Cruise in his nearly 25-year career has starred in such films as "Rain Man," "Jerry Maguire" and the upcoming Steven Spielberg remake of "War of the Worlds."
Holmes is best known for starring in the TV show "Dawson's Creek," and the movies "Wonder Boys" and "Pieces of April." She will co-star with Christian Bale in this summer's "Batman Begins."