Planned Parenthood said Richards would depart before the end of the year.
"Leading Planned Parenthood over the last 12 years has been the honor of my lifetime," Richards said in a statement. "I'm deeply proud of the progress we've made for the millions of people Planned Parenthood health centers serve across the country each year."
She said she would turn her attention toward campaigning on behalf of Democrats seeking seats in the 2018 midterm elections.
"I will be leaving the organization well-positioned to serve and fight for our patients for a century more. Every day we see the incredible power that grassroots voices can have -- there has never been a better moment to be an activist," she said.
Richards' departure comes amid a tumultuous period for Planned Parenthood, which faced a congressional investigation in 2015 over allegations the organization sold fetal tissue. Testifying to Congress, she said videos purporting to show Planned Parenthood officials discussing the sale of such tissue were part of a "smear campaign" by opponents.
Richards said the videos were "deceptively edited videos released by a group that is dedicated to making abortion illegal."
Meanwhile, the federal government and some states have sought to withhold government funding from the organization over abortions provided at some of its facilities.
Naomi Aberly, chair of Planned Parenthood's Board of Directors, praised Richards for growth that happened under her leadership. Supporters grew from 3 million to 11 million during her time as president.
"Because of Cecile's leadership and the amazing team she has built, the organization is well-positioned to continue to fulfill our mission of delivering quality, accessible sexual and reproductive health care and ensuring reproductive freedom," Aberly said.
Richards, daughter of former Texas Gov. Ann Richards, also serves on the board of the Ford Foundation, which works to advance human welfare.