Matlock is chairman of the House Transportation Committee, but isn't generally an outspoken member of the GOP caucus. In a statement Tuesday, Matlock said he is the person to unite the at times fractured House Republicans.

"My primary goal is to help our caucus become what it was always meant to be; a caucus that stands for justice and truth, a caucus that has bold and creative ideas, a caucus that at its heart stands for the people of our great state," Matlock said in the statement.

"I am ready to guide us forward, unite our causes, and provide support to each of you."

Harwell spokeswoman Kara Owen said Harwell will run for speaker again, assuming she wins re-election in November. Harwell is focused on her own race and helping other incumbents win in the general election, Owen said.

Every two years both parties formally re-elect their caucus leaders. House Republicans have chosen Harwell as speaker since 2010. Before the start of the 2015 session she easily defeated a challenge from now-retiring Rep. Rick Womick.

Harwell has faced some criticism for how House leaders handled allegations against embattled Rep. Jeremy Durham, R-Franklin. She has defended her actions, pointing to the new sexual harassment policy adopted for the House and Senate and saying she had only rumors to act on before a Tennessean investigation published in January. Since The Tennessean reported three women received inappropriate text messages from Durham's cellphone, Harwell has called for the lawmaker's ouster and created a special committee to investigate Durham.

Matlock drew little attention during this year's legislative session, apart from when he offered a resolution that would allow the legislature to meet in a special session to override Gov. Bill Haslam's veto of the bill making the Bible the official book of Tennessee. That resolution ultimately failed in the House.

Rep. Cameron Sexton, R-Crossville, said he talked to Matlock, who was trying to decide whether he should run for speaker, on Monday.

Sexton, who earlier this year was appointed by Harwell to serve as chairman of a special committee to examine the state's health care expansion options, said he told Matlock that he needed to "take his time and make sure everything that everybody was saying was accurate."

When asked to elaborate, Sexton said several lawmakers have been making statements about the Durham investigation and how it was handled. "One thing you learn down in the plaza is people aren’t afraid to try to turn a rumor into a fact," he said.

Despite saying he liked Matlock as a person, Sexton said he believes Harwell has been an effective speaker.

"I plan on supporting the speaker," he said.

Rep. Steve McDaniel, R-Parkers Crossroads, said he fully supports Harwell and he is "completely surprised" by Matlock's decision to challenge her. Harwell appointed McDaniel as chairman of the four-member legislative committee to investigate Durham.