The two parties, with a third smaller partner, have agreed a tie up for general elections later this year, and plan to unify as a single communist party following the polls.
"We had said before, after the signing of the peace deal, that Nepal should have a single communist party. We are now finishing that incomplete process," Maoist leader Pushpa Kamal Dahal said at a press conference announcing the deal.
The civil war ended in a peace deal in 2006 that saw rebel leader Dahal become Nepal's first post-war prime minister.
The 240-year-old Hindu monarchy was abolished two years later beginning the Himalayan nation's transformation to a secular republic.
Three main parties -- the Maoists, the Communist Party Nepal-Union Marxist Leninist (CPN-UML), and the Nepali Congress (NC) -- have since monopolised the political sphere, forming varying brittle coalitions with one another.
General elections set for next month will conclude the drawn-out peace process, allowing for the implementation of a new constitution that was agreed in 2015.
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