"I love this woman," Cruise says in an interview to air Monday on "Access Hollywood." "She's magnificent."
The couple were photographed together in Rome last month, where Cruise received a lifetime achievement award at the David di Donatello Awards, the Italian equivalent of the Oscars.
When asked why he appears to be less inhibited about showing his affection for Holmes in public than in his past relationships, Cruise tells "Access Hollywood" co-anchor Billy Bush: "I am so happy and I am not going to pretend or hide it or be shy. This woman is magnificent."
Cruise's marriages to Mimi Rogers and Nicole Kidman ended in divorce. He dated Penelope Cruz, but the pair split last year. Holmes and actor Chris Klein recently called off their engagement, after dating for five years.
The 42-year-old Cruise says he shares many common interests and hobbies with the 26-year-old Holmes.
"We go scuba diving together," he says. "She likes all the stuff that I love to do, she's funny and smart."
He added: "I've always seen how talented she was."
Cruise stars in Steven Spielberg's "War of the Worlds" and Holmes co-stars with Christian Bale in "Batman Begins." Both films open next month.