Cunningham faced a scandal during his campaign over sexually-charged text messages he admitted to sending to a married woman who was not his wife.
Tillis currently holds 48.7 percent of the vote to Cunningham's 46.9 percent, with 93 percent of the total vote counted.
Sen. Thom Tillis Says He Expects to Return to Capitol for Supreme Court Vote after Coronavirus Diagnosis
The senator announced Friday that he tested positive for the coronavirus after GOP Senator Mike Lee of Utah also tested positive.
“I have hurt my family, disappointed my friends, and am deeply sorry,” the Democratic candidate said in a statement.
North Carolina is the swing state where Trump is performing the best against Biden, followed closely by Florida.
North Carolina is one of the key states that could determine control of the U.S. Senate in November.
Cal Cunningham's lead is shrinking.
Sen. Tillis Says Fellow North Carolina Republican Burr ‘Owes Everybody an Explanation’ on Self-Dealing, Insider Trading Allegations
While he maintains his innocence, Burr has asked the Senate Ethics Committee to conduct a review of his actions.
Senator Thom Tillis (R., N.C.) reversed himself Thursday after vowing to support a resolution condemning President Trump's national emergency declaration.