The parties, however, failed to agree on how top positions like the President, Prime Minister and Speaker of the Constituent Assembly would be shared, the Kathmandu Post reported.
The two parties, which had been in informal talks for the last few days, came up with a three-point agreement at a meeting yesterday.
In the agreement signed by NC President Sushil Koirala and CPN-UML Chairman Jhala Nath Khanal, the parties expressed commitment "to respect the people's verdict in the election" and to complete drafting of a new constitution within the stipulated time of one year.
"We respect the fresh verdict reflected in the election and agreed to go ahead in unison to complete the unfulfilled political responsibilities," the agreement said.
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The UCPN (Maoist), which was the largest party after the 2008 election, has refused to take the seats it secured under the proportional representation category, alleging that widespread rigging was behind their disappointing performance in the November 19 polls.
The Maoists have been refusing to join the CA unless an independent commission is formed to probe the "poll irregularities".
NC General Secretary Krishna Prasad Sitaula said, "Winning or losing the election is always natural in periodic elections. The Maoists have no other alternative but to accept the election result. Polls were not rigged."
Situala hoped that the new CA will be constituted by December-end.
The Nepali Congress, one of the country's oldest parties, won 196 of the 575 seats up for grabs in the November 19 polls, pushing the former ruling Maoists into third place.