The couple said in a statement released Thursday through publicist Jessica Berger that they're "excited and incredibly happy" about their engagement. They didn't announce a wedding date.
The 36-year-old Lachey was previously married to Jessica Simpson, and the two starred in an MTV reality show about their lives together, called "Newlyweds: Nick & Jessica." Lachey now serves as host of NBC's "The Sing-Off."
The 29-year-old Minnillo is the host of ABC's "True Beauty."
The engagement was first reported by Us magazine.