McGill, who served in a state Senate from 2010 until 2014, when he decided to forego a reelection campaign.
The former legislator is one of four Republicans who are likely to mount a challenge to the 81-year-old Shelby, who reaffirmed he will again seek the office by filing with the state elections chief ahead of a November 6 deadline.
Shelby, first elected by statewide in 1986, is pursuing a sixth term in the Senate. He says his experience and seniority are assets for Alabamians.
“I am running for the United States Senate because I’m not done fighting for Alabama,” Shelby said in a recent statement. “My unmatched record of proven, conservative leadership puts me in the best position to stand up for Alabamians against big government policies in Washington. I have always and will continue to put Alabamians first.”
McGill, perhaps best known for claiming he was visited by strippers in the middle of the night during his 2010 campaign for the state Senate, will make his announcement in front of the Jackson County Courthouse.