The parties have reached an understanding for dividing the country into six provincial units during a crucial meeting this evening, according to Nepali Congress sources.
However, the deal is yet to be formally signed. Details of the proposed agreement have also not been made public.
There will be two provinces in the southern Terai plains in the new federal model.
Adopting a federal structure is one of the key issues on which political parties were negotiating for months.
Also Read
Once the deal is signed, the Constitutional Political Dialogue and Consensus Committee meeting slated for Friday night will endorse the deal reached among the parties.
With the agreement in place, constitution writing will enter the final phase.
Top leaders of Nepali Congress, CPN-UML, Unified CPN-Maoist and Madhesi Peoples Rights Forum attended the meeting at Singhdurbar secretariat here.