Energy Secretary Steven Chu will resign from President Barack Obama's Cabinet in coming weeks, he told Energy Department staff in a letter on Friday.
Chu, who turns 65 this month, was a leading advocate in the Obama administration for alternative energy development, making him a target of the fossil fuel industry and its conservative supporters in Congress.
He was a co-recipient of the Nobel Prize for Physics in 1997 and headed the Department of Energy's Lawrence Berkeley National Lab and taught at the University of California before becoming energy secretary in 2009.
"I informed the president of my decision a few days after the election that Jean and I were eager to return to California," Chu said in the letter. "I would like to return to an academic life of teaching and research, but will still work to advance the missions that we have been working on together for the last four years."
He said he would stay on through an upcoming government energy research summit at the end of February, adding: "I may stay beyond that time so that I can leave the department in the hands of the new secretary."
A statement by Obama thanked Chu for his "dedicated service," saying he "brought to the Energy Department a unique understanding of both the urgent challenge presented by climate change and the tremendous opportunity that clean energy represents for our economy."
Chu "helped my administration move America towards real energy independence," Obama's statement said, citing a doubling in renewable energy use, reductions in dependence on foreign oil and progress toward creating green energy jobs.
At a White House event later Friday honoring Medal of Science winners, Obama mentioned Chu's planned departure, calling it "a loss for us."
He also praised Chu for "designing a cap to plug a hole in the middle of the Gulf of Mexico when nobody else could figure it out," referring to the Deepwater Horizon oil spill of 2010.
Critics blamed Chu for government backing of failed clean energy ventures led by the collapse of Solyndra. The solar panel maker went bankrupt in 2011 after receiving more than $500 million in federal financing under an Obama administration effort to accelerate such investments.
"The direction the Department of Energy has taken under his leadership has been disconcerting," said Rep. Darrel Issa, R-California, adding that he considered "taxpayer losses on projects like Solyndra and the department's deeply misguided effort to use taxpayer dollars as an investment bank for unproven technologies to be the most problematic aspects of his legacy."
In his letter to Energy Department staff, Chu called his stint as energy secretary the "greatest privilege" of his life.
He cited the creation of the Advanced Research Projects Agency-Energy, a government effort to support energy technology development, as a major accomplishment, along with steps that he said have doubled production of wind and solar energy.
Chu's letter also defended the loan program linked to Solyndra, noting it was started in the Bush administration and supported 33 projects that he said generated $55 billion in economic investment.
"While critics try hard to discredit the program, the truth is that only 1% of the companies we funded went bankrupt," Chu wrote, later adding that "the test for America's policy makers will be whether they are willing to accept a few failures in exchange for many successes."
Chu also called in the letter for stronger U.S. action on climate change in the face of unrelenting opposition by the fossil fuel industry and conservatives in Congress.
"While we cannot accurately predict the course of climate change in the coming decades, the risks we run if we don't change our course are enormous," Chu's letter said. "Prudent risk management does not equate uncertainty with inaction."
In particular, he wrote that despite the improved ability to find and develop fossil fuel resources, the nation should work harder to develop viable alternatives.
"As the saying goes, the Stone Age did not end because we ran out of stones; we transitioned to better solutions," Chu wrote.