He spoke in Munich, Germany, where top diplomats from more than a dozen countries, including the United States and Russia, met to hammer out a deal.
"I'm pleased to say that as a result today in Munich, we believe we have made progress on both the humanitarian front and the cessation of hostilities front, and these two fronts, this progress, has the potential -- fully implemented, fully followed through on -- to be able to change the daily lives of the Syrian people," Kerry said.
"First, we have agreed to accelerate and expand the delivery of humanitarian aid beginning immediately," he told reporters.
"Second, we have agreed to implement a nationwide cessation of hostilities to begin in a target of one week's time. That's ambitious, but everybody is determined to move as rapidly as possible to try to achieve this."
CNN Global Affairs Correspondent Elise Labott described the move as both significant and tenuous. She noted the importance of Kerry's use of the phrase "cessation of hostilities," as opposed to the word ceasefire.
"This is an incremental step-by-step process, the first building block here, the humanitarian aid," said CNN International Diplomatic Editor Nic Robertson.
"That cessation that comes begets, possibly, better stronger talks (and) ultimately ... maybe a ceasefire," he said.
'Actions on the ground'
Any potential ceasefire would not apply to terrorist organizations operating in Syria. And Kerry stressed that the longer the conflict persists there, the more extremists have to gain.
Kerry also said that the real test of talks will be whether all the parties involved honor their commitments and implement them in reality. Ending the five-year civil war will require a plan for a political transition, he said.
The Syrian uprising began in March 2011. At least 250,000 people have died and 12 million displaced because of the conflict, according to the United Nations.
"What we have here are words on paper. What we need to see in the next few days are actions on the ground," Kerry told reporters.
His point was echoed by Russian Foreign Minister Sergey Lavrov, who spoke at the same news conference in Munich.
Lavrov said that a ceasefire would be difficult but characterized what was announced Friday as a "step forward."
"We have a common determination to reduce the suffering of the Syrian people," he said.