The 37-year-old actor proposed to Santana on a sailboat in the middle of the Hudson River in New York this week when they were celebrating her birthday, reported Us Weekly.
"It's been a long time coming, but we couldn't be happier," he said.
Metcalfe, and 33-year-old Santana have been together for over 10 years.
The couple were previously forced to deny reports they were engaged.
Metcalfe previously dated Girls Aloud singer Nadine Coyle.