Environmental Protection Agency chief Lisa Jackson said Thursday she would leave her post early next year, following a tumultuous four years in which she pursued the first US greenhouse-gas regulations and battled Republican efforts to limit her agency's powers.
Ms. Jackson has served in the role since early in President Barack Obama's first term.
She said in a statement that she "will leave the EPA confident the ship is sailing in the right direction, and ready in my own life for new challenges, times with my family and opportunities to make a difference."
She said the agency has made "historic progress" on cleaning up pollution and protecting the environment and public health. She said she would depart after Mr. Obama's State of the Union address.
The president on Thursday thanked Ms. Jackson for "her tireless efforts to benefit the American people" and said "under her leadership, the EPA has taken sensible and important steps to protect the air we breathe and the water we drink."
Republicans and industry groups often criticized Ms. Jackson, saying her agency's regulations were killing jobs and raising uncertainty for business.
Scott Segal, a partner at Bracewell & Giuliani who represents utilities that use coal, said Thursday that Ms. Jackson "presided over some of the most expensive and controversial rules in agency history."
At one point, Ms. Jackson's aggressive approach to curbing pollution ran into opposition from her boss. In September 2011, Mr. Obama overruled Ms. Jackson and ordered the administration to withdraw a proposed tightening of the national standard for smog pollution, even though Ms. Jackson had said a stricter standard was necessary to protect public health.
Ms. Jackson and her deputies testified before Congress regularly, most often before House Republicans who pushed bills that would curb the EPA's power. The bills were blocked by Senate Democrats.
Ms. Jackson pushed back against the criticism, asserting for instance that her power plant regulations were preventing soot pollution that could harm children or the elderly. She said the agency's regulations created jobs because US companies could be leaders in pollution-control technologies.
In February 2011, Leo Gerard, international president of the United Steelworkers, gave Ms. Jackson a pair of boxing gloves as a birthday gift, citing her many tussles with lawmakers.
Ms. Jackson generally won high praise from environmental groups.
"Health and environmental advocates will definitely miss her," said Frank O'Donnell, president of the advocacy group Clean Air Watch. "She has been a real champion for clean air."
Ms. Jackson in 2009 made a formal finding that greenhouse gas emissions posed a danger to public health and began the first push to regulate them. As part of that effort, the EPA adopted new national standards for vehicle fuel efficiency and proposed regulations that would essentially ban new coal-fired power plants unless they use a carbon capture technology that is not yet commercially viable.
She also led the agency as it made final long-pending limits on pollutants such as mercury from coal-fired power plants and industrial boilers that burn coal for electricity.
While Ms. Jackson's EPA accomplished much of its clean air agenda, it also suffered some setbacks.
In August, the US Court of Appeals for the District of Columbia Circuit threw out a regulation to curb air pollution that wafts across state lines, sending Ms. Jackson back to the drawing board on one of her major accomplishments.
In March, a federal judge reversed the agency's 2011 decision to revoke a permit from a large mountaintop coal mine in West Virginia. The judge said the agency overstepped its authority.
Ms. Jackson clashed with lawmakers on the agency's oversight of hydraulic fracturing, or fracking, the technology that has helped fuel a boom in US oil and gas production. The EPA earlier this year adopted rules limiting air pollution from natural gas wells. Its scientists said they found a link between fracking and groundwater contamination in Wyoming, a conclusion the industry disputes.
Ms. Jackson's successor is likely to oversee the completion of the agency's yearslong study of fracking's impact on groundwater and any resulting regulatory push, as well as regulations limiting greenhouse-gas emissions from hundreds of existing US coal plants. Mr. Obama's choice could be an early signal of how he plans to approach environmental issues in a second term.