The mediators said the ceasefire from Saturday morning was "an effort to break the cycle of violence" between Sudan's army and the paramilitary Rapid Support Forces (RSF), which began battling each other eight weeks ago, sparking a major humanitarian crisis.
The conflict has displaced more than 1.9 million people, 400,000 of whom have crossed into neighbouring countries.
The urban area around Sudan's capital Khartoum, home to at least five million people, has been turned into a war zone and unrest has also flared in the conflict-scarred western region of Darfur.
Fighting continued on Friday, with residents reporting artillery fire and clashes in the north of Omdurman, across the confluence of the River Nile from Khartoum, and air strikes in Bahri, a third adjoining city that makes up the wider capital.
"There are heavy strikes near us and bullets from every direction in Al-Thawra neighbourhood in Omdurman," said Sanaa Ahmed, a 24-year-old resident.
"We are really afraid and we don't know what to do."
Medical charity MSF said fighting had intensified significantly in Khartoum since Tuesday, resulting in a surge of patients to a hospital where it is working.
Another city where the conflict has triggered clashes is El Obeid in North Kordofan State southwest of Khartoum, which lies on a main route between the capital and Darfur, the RSF's power base.
A doctors' group said in a statement that the city had been suffering from water outages for more than a month, shortages of food, medicine and fuel and two weeks of power cuts.
Twelve kidney dialysis patients had died due to the effects of the war and dozens more were at risk, it said.
The ceasefire is due to start at 6am local time on Saturday.
The two sides agreed to "refrain from prohibited movements, attacks, use of aircraft or drones, aerial bombardment, artillery strikes, reinforcement of positions and resupply of forces, and will refrain from seeking military advantage during the ceasefire," a Saudi-US statement read.
They also agreed to allow delivery of humanitarian assistance, it said.
Both sides have broken a string of ceasefire agreements, including a 12-day truce deal that expired on June 3 and was brokered by Saudi Arabia and the US at talks in Jeddah.
Fighting subsided slightly during the period of that truce deal and limited amounts of humanitarian relief were delivered, although aid agencies say their operations have been badly impeded by bureaucratic controls, fighting and looting of aid supplies.
The army said last week that it was pulling out of the Jeddah talks, although both sides kept delegations in the Saudi city for consultations.
If the parties fail to observe the new ceasefire, "facilitators will be compelled to consider adjourning the Jeddah talks," the Saudi-US statement said.
The army confirmed in a statement that it had agreed to the 24-hour ceasefire while asserting "its right to respond to any violations".
The RSF said in a statement it was committed to respecting the truce.
The conflict in Sudan derailed the launch of a transition towards civilian rule four years after a popular uprising ousted strongman president Omar al-Bashir.
Sudan's army and the RSF fell out over the chain of command and military restructuring plans under the transition.
"We have provided both parties numerous opportunities to end this senseless war," the US State Department's Bureau of African Affairs said on Twitter.
"We call on both sides to adhere to the commitment made today for a 24-hour ceasefire, which would allow Sudanese people to receive critical humanitarian assistance."
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