The United States has fulfilled "the goals that we set out to achieve" in Afghanistan, according to American Secretary of State Antony J. Blinken.
Speaking prior to a meeting with NATO Secretary General Jens Stoltenberg in Brussels, the US Foreign Secretary said it was "time to bring our forces home".
The May deadline had been negotiated with the Taliban by the Trump administration.
Mr Blinken said it was an "important moment" for NATO, adding: "Almost 20 years ago, after the United States was attacked on 9/11, together, we went into Afghanistan to deal with those who attacked us, and to make sure that Afghanistan would not again become a haven for terrorists who might attack any of us.
"Together, we have achieved the goals that we set out to achieve. And now, it is time to bring our forces home."
The US Secretary of State also suggested the alliance would exit Afghanistan "together".
"We will work very closely together, in the weeks and months ahead, on a safe, deliberate and coordinated withdrawal of our forces from Afghanistan," he continued.
Watch: A recent history of British forces in Afghanistan.
"Even as we do that, our commitment to Afghanistan, to its future, will remain."
In a February 2020 agreement with the administration of then-president Donald Trump, the Taliban agreed to halt attacks and hold peace talks with the Afghan government, in exchange for a US commitment to a complete withdrawal by May 2021.
The deal included NATO forces deployed to the country.
Over the past year, US military commanders and defence officials have said that attacks on American troops have largely been paused, but they say the Taliban has increased attacks on Afghans.
The UK currently has about 750 personnel in Afghanistan, having had a presence there since 2001.
Defence Select Committee chair Tobias Ellwood has warned that the US decision to withdraw its troops from Afghanistan by the autumn risks "losing the peace".
Mr Ellwood said the move would make it "very difficult" for British troops to remain in the battle-ravaged country, warning that a consequent vacuum could allow extremists to "regroup".
Cover image: US Army.