Kerry told an international conference in Brussels to raise funds for the Western-backed Afghan government that the Taliban could not win on the battlefield.
He pointed to a peace agreement announced last week with the Hezb-i-Islami militant group headed by Hekmatyar, "one of the country's most notorious figures."
"This a model for what might be possible ... I think the message from every person here would be to the Taliban, take note," Kerry said.
"There is a path forward towards an honourable end to the conflict that the Taliban have waged - it is a conflict that cannot and will not be won on the battlefield. A political settlement negotiated with the Afghan government is the only way to end the fighting, ensure lasting stability, and achieve a full drawdown ultimately of international military forces, which is their goal," he said.
"Their goal of ridding Afghanistan of external forces will not occur by ... the continued insurgency, it will come though peace," Kerry added.
Last week's agreement requires Hekmatyar to cease violence, cut all ties with international militant groups, and accept the Afghan constitution, including its guarantee of rights for women and minorities.
"In return for keeping these commitments, Hekmatyar's group will be able to emerge from the shadows to rejoin Afghan society," Kerry said.
Leaders and officials pose for a family photo during the Conference on Afghanistan in Brussels on Wednesday.
The agreement will grant Hekmatyar amnesty for past offences and the release of certain Hezb-i-Islami prisoners. The Kabul government also agreed to press for the lifting of international sanctions on Hekmatyar.
The Brussels conference is expected to pledge more than $3bn a year of development assistance to the Afghan government and Kerry said this was as sign that the world would stand by Afghanistan, where the United States and its allies have been battling the Taliban since 2001.
"The Taliban and their allies cannot wait us out ... We will not abandon our Afghan friends," Kerry said.
Hekmatyar is a controversial figure, having been accused of killing or wounding thousands when his troops fired on Kabul during the civil wars of the 1990s. He has been designated a "global terrorist" by the United States.
During the 1980s, however, he received significant aid from the United States, as well as from Pakistan and Saudi Arabia, to fight Soviet forces occupying Afghanistan.
Compared to other militant groups like the Taliban or Islamic State, Hezb-i-Islami has played a relatively small role in the insurgency recently and analysts say the accord is mostly symbolic.
