Martin Griffiths told the Security Council on Friday that a speedy presence in the field is "an essential part of the confidence" needed to accompany the implementation of Thursday's agreement between warring parties.
Griffiths emphasised the importance of the Houthi decision to withdraw Hodeidah and its three ports, which serve as a major lifeline for the 18 million Yemenis who live in the rebel-held territory.
As part of the agreement, the ports of Hodeidah, Saleef and Ras Isa would fall under the control of "local forces", who would then send the ports' revenue to the country's central bank.
Griffiths said agreement and other confidence-building measures will help alleviate the suffering of millions of Yemenis.
"After two and a half years of missed opportunities, I think it's fair to say that the political process to find a comprehensive solution to the conflict in Yemen has finally resumed," Griffiths said.
"This is no small achievement, made possible first and foremost by the commitment of the parties and the credit goes to them.
"I was extremely impressed by their dedication. All made concessions, all engaged in depth and at length, intensively and in good faith."
The week-long negotiations were the first between Yemen's internationally recognised and Saudi-backed government of President Abd-Rabbu Mansour Hadi and Houthi rebels who seized control of the capital Sanaa in 2014.