In a statement posted to Twitter, Mastriano, who former President Donald Trump endorsed, said the results of the midterm elections had not gone the way Republicans had hoped and "fought so hard for."

"In all, we received votes from almost 2.2 million Pennsylvanians, and I thank every one of you, from the bottom of my heart," he said.

Shapiro was projected as the winner in the race for governor late on election night by NBC News. The Associated Press also called the race in favor of Shapiro on election night, when Shapiro had 54.42 percent of the vote, or 2,571,668 votes, and Mastriano 43.74 percent. As of Sunday, Shapiro has 56.3 percent of the vote compared to Mastriano's 41.9 percent.

"We gave this race everything we have," Mastriano said. "Difficult to accept as the results are, there is no right course but to concede, which I do, and I look to the challenges ahead. Josh Shapiro will be our next governor, and I ask everyone to give him the opportunity to lead and pray that he leads well."

Mastriano's statement comes nearly five days after NBC's initial projection.