Byrne, a Democrat who joined the Republican Party in 1997, won 34.6 percent of the vote, AL.com reported, citing unofficial results. He must compete in a runoff against Dean Young, a businessman and former aide to Roy Moore, the chief justice of the Alabama Supreme Court, who became nationally known for refusing to take down a "Ten Commandments" monument.
Young won 22.9 percent of the vote, followed by state Rep. Chad Fincher with 15.6 percent and Quin Hillyer, a conservative columnist with 13.9 percent. Hillyer, who had won an endorsement from former U.S. Sen. Rick Santorum, R-Pa., for his candidacy, immediately backed Byrne in the runoff.
The election will replace Jo Bonner, a Republican who resigned from Congress to take a job with the University of Alabama. The winner of the Republican primary in the conservative district is almost certain to win the seat.
Byrne ran unsuccessfully for governor in 2010, losing a runoff after being the top vote getter in the Republican primary.