Ismail Ould Cheikh Ahmed said he had received assurances from all Yemeni parties for such a move.
Yemeni President Abdrabbuh Mansour Hadi's forces have been fighting Houthi rebels, who control the capital Sanaa.
Mr Ahmed's announcement follows international alarm over the deaths of 140 people in a Saudi airstrike which hit a funeral gathering in Sanaa.
Saudi officials say the airstrike in the capital earlier this month should have hit Houthi rebel leaders, but erroneous intelligence meant that the wrong site was targeted.
The US, Britain and the UN peace envoy to Yemen have all been urging warring parties in the country's civil war to declare an immediate ceasefire.
In a statement, Mr Ahmed said he had received "assurances from all Yemeni parties of their recommitment to the Terms and Conditions of the Cessation of Hostilities of 10 April 2016".
He said the measure would "re-enter into force at 23:59 Yemen time (20:59 GMT) on 19 October 2016, for an initial period of 72 hours, subject to renewal".
Mr Ahmed said this "will spare the Yemeni people further bloodshed and will allow for the expanded delivery of humanitarian assistance".
Earlier, Yemeni Foreign Minister Abdel-Malek al-Mekhlafi said that President Hadi had agreed to the 72-hour truce.
But the minister stressed that any ceasefire must also feature a promise by the rebels to end the siege of Taez, Yemen's third-city.
The conflict in Yemen pits forces loyal to the internationally recognised government of President Hadi against the rebels. The coalition led by Saudi Arabia accuses Iran of backing the rebels and supports the president.
The war has killed nearly 7,000 people in addition to wounding more than 35,000 and displacing at least three million since March last year, according to the UN.