|Katie Holmes, left, and Tom Cruise|
Cruise said he chose the Paris landmark because it is "very beautiful and romantic."
Katie Holmes was wearing a large diamond engagement ring when the two appeared at a news conference on Cruise's new movie, War of the Worlds.
Both deny speculation that their romance is a stunt to promote their films.
It will be a third marriage for 42-year-old Cruise, whose former wives are actresses Mimi Rogers and Nicole Kidman. It will be the first for 26-year-old Holmes, who currently stars in Batman Begins.
Some information for this report provided by AP, AFP and Reuters.