The team led by Patrick Cammaert, a retired Dutch general, made their first stop in Aden where forces loyal to fugitive former president Abd Rabbuh Mansour Hadi, a close ally of Riyadh, are based.
The official will later travel to Sana’a and onwards to Hudaydah, AFP reported.
The team's arrival comes a day after the UN Security Council unanimously approved a resolution authorizing the deployment of observers to Hudaydah, a lifeline port city which serves as the entry point for the majority of imports to the impoverished Arab country.
The UN team is due to secure the functioning of the port as well as supervise the withdrawal of fighters from the city.
The resolution submitted by Britain also endorses the outcome of UN-brokered peace negotiations in Sweden last week, where the warring parties agreed to the Hudaydah truce which came into effect Tuesday.
The text approved by the Security Council "insists on the full respect by all parties of the ceasefire agreed" for Hudaydah.
It authorizes the United Nations to "establish and deploy, for an initial period of 30 days from the adoption of this resolution, an advance team to begin monitoring" the ceasefire, under Cammaert's leadership.