Undersecretary of Defense for Policy Colin Kahl holds a news briefing in August at the Pentagon about military aid for Ukraine. (Lisa Ferdinando/Department of Defense)

WASHINGTON — Colin Kahl, a top policymaker at the Pentagon and adviser on sending U.S. aid to Ukraine, will leave his post in the summer, the Defense Department said Wednesday.

Kahl, 51, who has served as undersecretary of defense for policy since April 2021, has been involved in decision-making about U.S. military aid to Ukraine in the past several months. He also served as national security adviser to then-Vice President Joe Biden between 2014 and 2017 during former President Barack Obama’s administration.

“Kahl announced that he will step down from his position in mid-July,” Defense Secretary Lloyd Austin said Wednesday. “Since his appointment, Kahl has been a trusted adviser and a resolute leader in our mission to safeguard American interests.”

Austin said he has relied on Kahl for advice in several areas, including Ukraine, Chinese influence in the Indo-Pacific region, support for American allies in the Middle East, emerging defense technologies and clandestine information warfare online.

“His strategic insights, deep understanding of international relations and staunch commitment to strengthening our national defense have been crucial in shaping our policies, seizing geopolitical opportunities and tackling a range of challenges around the world,” the defense secretary said.

Kahl’s career in Washington stretches back to 2009 when he was deputy assistant secretary of defense for the Middle East in the Obama administration, a role that he held for two years. In 2015, he became a contributor to the Joint Comprehensive Plan of Action — also known as the Iran Nuclear Deal, which was struck by the U.S. and several other countries to get Tehran to shelve its nuclear weapons research. Former President Donald Trump pulled the U.S. out of the deal in 2018, and Biden has yet to rejoin, though he has said he wants to do so.

In his role as undersecretary of defense for policy, Kahl was responsible for overseeing how the Pentagon handles military threats from potential adversaries such as Russia, China, Iran and terrorist groups such as the Islamic State.

“Under his leadership, the [Pentagon] rolled out its National Defense Strategy, focusing on the pacing challenge of the People’s Republic of China, the acute threat of Russian aggression and other dangers. And he has helped ensure steadfast U.S. support for Ukraine through billions of dollars of security assistance since the beginning of Russia’s unprovoked war of choice,” Austin said. “Our department is stronger and better prepared for future security challenges because of Colin’s distinguished service.”

When Kahl accepted the job in 2021, he took a two-year leave of absence from his position as a tenured political science professor at Stanford University in California.

Kahl’s successor has not been named and must be nominated by the president and confirmed by the Senate.