Sen. Rand Paul of Kentucky and Oklahoma Gov. Mary Fallin have also been selected to speak at the convention, USA Today reported Tuesday.
Santorum is the first of Mitt Romney's former rivals for the 2012 Republican nomination to be announced as a speaker.
Paul is a Tea Party favorite and the son of Rep. Ron Paul of Texas who also ran for the GOP nomination.
No dates or times for the speakers had been announced.
The GOP convention will be held Aug. 27-30 in Tampa, Fla.
Among the speakers announced earlier are former Arkansas Gov. Mike Huckabee, former Secretary of State Condoleezza Rice, Sen. John McCain and Govs. Nikki Haley of South Carolina, Susana Martinez of New Mexico, John Kasich of Ohio and Rick Scott of Florida.