The Zaydi-Shia Houthi rebels and the General People's Congress of former President Ali Abdullah Saleh have agreed to "form a supreme political council of 10 members", according to a statement.
The announcement is the latest sign that UN-brokered peace talks with the government had failed, and the group did not name the council's members.
"The aim is to unify efforts to confront the aggression by Saudi Arabia and its allies," the statement said in reference to the Riyadh-led Arab coalition that launched a military campaign to support Yemen's President Abd Rabbo Mansour Hadi.
The job of the council will be to "manage state affairs politically, militarily, economically, administratively, socially and in security".
The rebels overran Sanaa in September 2014 and expanded their control to other parts of Yemen.
In February 2015 they set up a "Supreme Revolutionary Council" to run the country after they announced a dissolution of the government and parliament.
UN-sponsored talks between the rebels and representatives of Hadi's government, which began in April, have failed to make headway.
The indirect negotiations being held in Kuwait were launched after the United Nations secured an agreement on a ceasefire in the war-torn country.
More than 6,400 people have been killed in Yemen since the Saudi-led coalition intervened in support of Hadi's government.
Another 2.8 million people have been displaced and more than 80 percent of the population urgently needs humanitarian aid, according to UN figures.