Khalilzad in a series of Twitter posts officially confirmed his resignation from the post of special representative of the US to Afghanistan's reconciliation and welcomed his deputy Thomas West to the post.
US Secretary of State Antony Blinken had praised him and expressed gratitude for all his efforts as their special envoy to his native country.
Khalilzad said that it was an honour for him to serve the people of America and added to remain committed to peace and stability in Afghanistan.
"I thank all my colleagues at the State Department, Pentagon, and intelligence community who joined me on this mission," reads a tweet.
He served as US special representative for nearly three years and got the US-Taliban agreement signed but failed to make the Taliban and Afghan government reach an agreement.
Former Afghan officials and Afghan people criticize his mission though the Taliban foreign ministry said that they made progress with Khalilzad.