Tillis campaign spokesman Daniel Keylin said in an email that Romney was headlining the private event in Charlotte on Tuesday night.
The 2012 Republican presidential nominee and former Massachusetts governor has publicly supported Tillis since endorsing him on the eve of the May GOP primary.
Romney appeared recently on behalf of Republican House and Senate candidates in New Hampshire and Florida, and he was scheduled to appear at campaign events Tuesday in West Virginia.
Romney won North Carolina in the 2012 presidential election with just over 50 percent of the vote.
Tillis faces Democratic U.S. Sen. Kay Hagan in November.