Sources close to Jackson told The Washington Post she has not yet decided on another job. Jackson had been expected to leave after President Barack Obama's first term.
Jackson said she would leave after Obama's State of the Union message, expected to be delivered Jan. 29.
Some Republicans accused Jackson of a "war on coal" because of stricter regulations on emissions from power plants and stronger curbs on soot. The same rules and the first limits on emissions of greenhouse gases by motor vehicles were praised by environmentalists.
Obama released a statement praising Jackson's work at EPA and calling her an "important part of my team."
"Over the last four years, Lisa Jackson has shown an unwavering commitment to the health of our families and our children," he said. "Under her leadership, the EPA has taken sensible and important steps to protect the air we breathe and the water we drink, including implementing the first national standard for harmful mercury pollution, taking important action to combat climate change under the Clean Air Act, and playing a key role in establishing historic fuel economy standards that will save the average American family thousands of dollars at the pump, while also slashing carbon pollution."
Jackson, 50, a graduate of Tulane University, earned a master's in chemical engineering at Princeton, worked for the EPA for 16 years, and then served as New Jersey's commissioner of environmental protection.