Land told The Associated Press in a written statement that she wants to focus her attention on the campaign. The former Michigan secretary of state was elected for a four-year term to the RNC at a state Republican convention in 2012.
"I had planned to step down from the Republican National Committee after the (August) primary in order to focus our full attention on the general election. Now that it doesn't look like there is a primary, the timing makes sense," Land said. "It is time to move forward as the candidate for U.S. Senate."
Michigan's other RNC elected member is Dave Agema, who has refused to step down after making anti-gay and anti-Muslim comments, despite calls from many top Republicans to resign. The Agema controversy has been awkward for Land politically, though she did not mention it in her Friday resignation statement.
She initially expressed disagreement with Agema but did not ask him publicly to step down until shortly after RNC Chairman Reince Priebus and Michigan Republican Party Chairman Bobby Schostak called for his resignation a week ago.
The Michigan Democratic Party earlier this week asked if Land would campaign with Agema after he praised her on Facebook.
It is up to the 113-member Michigan Republican State Committee to choose Land's replacement, possibly as early as its Feb. 14-15 meeting if the rules allow it.
"We thank Terri Lynn Land for her service as National Committee Woman, and while we are saddened to receive this news, we understand and support her decision," Schostak said in a statement.
Land's likely Democratic opponent is U.S. Rep. Gary Peters.