Yemen's National Dialogue Conference has agreed a document on which the new constitution will be based.
President Abdrabbuh Mansour Hadi will reveal details of the rival political, tribal, religious and social groups' vision for a new political system at the end of the conference on Saturday.
It is believed to include dividing the country into a number of regions that enjoy semi-autonomy.
Earlier, gunmen killed a representative of the Houthi rebel movement in Sanaa.
Ahmed Sharaf al-Din, a law professor, was shot dead as he drove from his house in the capital to the hotel where the National Dialogue conference is being held, officials said.
He was the second Houthi envoy to the talks to be killed.
The Houthis, a group of Zaidi Shia Muslims who draw their name from their late leader, launched a six-year rebellion against the central government in 2004 that left thousands of people dead in the north.
Since October they have been involved in clashes with ultraconservative Salafists and Sunni tribesmen allied to them in several northern areas despite a government-brokered ceasefire.
Addressing the National Dialogue Conference on Tuesday, President Hadi described Mr Sharaf al-Din as a "martyr" and said "forces of evil" were trying to halt Yemen's democratic transition.
The talks at a heavily-fortified five-star hotel in Sanaa, which began last March, were a key part of the agreement brokered by the UN and the Gulf Co-operation Council that saw long-time President Ali Abdullah Saleh hand over power to Mr Hadi in November 2011 after an uprising.
Mr Hadi was subsequently sworn in for a two-year term as president in February 2012 after an election in which he stood unopposed.
On Tuesday, delegates at the National Dialogue Conference agreed that Mr Hadi should remain in office until the new constitution has been approved and general elections held.
The president will head the committee that drafts the new charter.
He was also mandated to reshuffle the cabinet and restructure the consultative upper house of parliament, the Shura Council, to give greater representation to the south, where separatists have been demanding more autonomy, and to Zaidi Shia in the north.
"I did not take over a nation. I took over a capital where gunshots are continuous day and night, where roadblocks fill the streets. I took over an empty bank that has no wages and a divided security apparatus and army," Mr Hadi told the delegates.
"The National Dialogue document is the beginning of the road to build a new Yemen," he added.
The UN's special envoy for Yemen, Jamal Benomar, described the conclusion of the National Dialogue Conference as a "historic moment".
"After being on the brink of civil war, Yemenis negotiated an agreement for peaceful change, the only such in the region," he said.
"The National Dialogue established a new social contract and opened a new page in the history of Yemen, breaking from the past and paving the way for democratic governance founded on the rule of law, human rights and equal citizenship," he added.