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 are dating.
Both actors have had high-profile relationships.
Cruise's first two marriages, to actresses Mimi Rogers and Nicole Kidman, ended in divorce. He was dating actress Penelope Cruz until the pair split last year.
Holmes and actor Chris Klein - whose credits include "American Pie," "American Pie 2," "Rollerball," and "We Were Soldiers" - recently called off their engagement after five years as a couple.
Cruise, in his nearly 25-year career, has starred in numerous hits including "Top Gun," "Color of Money," "Rain Man," "Mission Impossible," "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."