The Environmental Protection Agency’s No. 2 guy is resigning after a career at the agency that spans two decades.

Bob Perciasepe, the agency’s deputy administrator, will lead an environmental advocacy group, Center for Climate and Energy Solutions.

“With his departure, EPA is losing its longest serving deputy – but more importantly a leader who poured his heart, soul and decades of experience into the agency’s mission every day,” said EPA Administrator Gina McCarthy in an e-mail to staff Thursday morning.

A Washington policy fixture, Perciasepe worked on clean air and clean water issues during the Clinton administration. He held a top job at the National Audubon Society, and in 2009 President Obama named him deputy at EPA.

When Obama’s first EPA administrator, Lisa Jackson, stepped down, some thought Perciasepe, who stepped in as acting head, would get the job. Instead, McCarthy was Obama’s pick, but the Loop reported then that the president may have personally called Perciasepe to ask him to stay on.

In a statement released by his new employer, Perciasepe said there is “opportunity and obligation to forge lasting climate solutions.”