Ryan Crocker, the US ambassador to Afghanistan, is set to step down from his post, according to the embassy in Kabul.
Tuesday's announcement comes after the conclusion of a NATO summit in Chicago during which the US and 50 allied nations, 28 of which are members of NATO, formalised an agreement to hand control of Afghanistan over to its own security forces by the middle of next year.
Victoria Nuland, State Department spokeswoman, cited health reasons for the the 62-year-old veteran envoy leaving his post in in the Afghan capital. Nuland would not specify the medical concerns that have led to Crocker's departure a year earlier than planned after he came out of retirement in 2011 to take the helm of the embassy at Barack Obama's personal request.
In a post on their official Twitter account, the US embassy in Kabul confirmed earlier reports of Crocker's departure, saying ambassador "Crocker has confirmed with regret that he will be leaving Kabul this summer".
Officials in Washington said he made his plans known to Obama during this weekend's NATO summit in Chicago.
Cameron Munter, US ambassador to neighbouring Pakistan, had announced the end of his diplomatic tour just weeks earlier.
Crocker, a six-time ambassador, had also served as envoy to Pakistan for three years starting in 2004, Iraq from 2007 to 2009, and Syria from 1998 to 2001.
He oversaw the reopening of the US embassy in Kabul in 2002, which had been closed during Taliban rule.
Crocker served in Iraq during a period in which violence dropped dramatically and the US and Iraq signed a military pact providing for the eventual withdrawal of all US forces.
For his turn as ambassador to Iraq, Crocker received the Presidential Medal of Freedom, the country's highest civilian honour, in 2009.
It is not immediately clear who will replace him, although officials said the most likely candidate is James Cunningham, a former ambassador to Israel and deputy UN envoy who is now one of the ex-ambassadors serving under Crocker in Kabul.
Crocker will leave after international donor conferences for Afghanistan are held in Tokyo and Kabul, Nuland said in a statement.
"Ambassador Crocker's tenure has been marked by enormous achievements," she said, listing the successful negotiation of a strategic partnership agreement with Afghanistan and the Chicago summit as highlights.