Roman Catholic Cardinal Timothy Dolan will give the benediction at the Republican National Convention.
The cardinal will offer the prayer on the night that Republican presidential candidate Mitt Romney accepts the GOP's presidential nomination.
Romney made the announcement in an interview with "The World Over Live" show on EWTN Catholic Network.
Dolan is president of the U.S. Conference of Catholic Bishops. He also leads the Roman Catholic archdiocese of New York.
The archdiocese is one of more than 40 Catholic groups suing the Obama administration over his mandate that employers provide health insurance that includes free birth control as a preventive service.
The rule exempts houses of worship but includes faith-affiliated employers such as hospitals, charities, and colleges.
Dolan's office said his appearance at the convention will not be an endorsement for Mitt Romney.
The GOP convention is scheduled to start Monday in Tampa, Fla.