Baradar, who heads the Taliban's political office, will be joined by Mullah Mohammad Yaqoob, the son of late Taliban co-founder Mullah Omar, and Sher Mohammad Abbas Stanikzai, in senior positions in the government.
"All the top leaders have arrived in Kabul, where preparations are in final stages to announce the new government," a Taliban official told Reuters.
Haibatullah Akhundzada, the Taliban's supreme religious leader, will focus on religious matters and governance within the framework of Islam, another Taliban source said.
Taliban seizing Kabul on 15th August, after sweeping across most of the country, have faced resistance in the Panjshir Valley, where there have been reports of heavy fighting and casualties.
Several thousand fighters of regional militias and remnants of the government's armed forces have massed in the rugged valley under the leadership of Ahmad Massoud, son of former Mujahideen commander Ahmad Shah Massoud.
While Taliban have spoken of their desire to form a consensus government, there are forecast that the interim government would be formed solely by Taliban members.
It would comprise 25 ministries, with a consultative council, or shura, of 12 Muslim scholars, the source added.
Also being planned within six to eight months is a loya jirga, or grand assembly, bringing together elders and representatives across Afghan society to discuss a constitution and the structure of the future government, the source said.
Western powers say they are prepared to engage with the Taliban and send humanitarian aid, but that formal recognition of the government and broader economic assistance will depend on action - not just promises - to safeguard human rights.
The United States, European Union and others have cast doubt on the movement's assurances. Many Afghans, especially women and those with connections to the former government or Western coalition forces, now fear for their security and even lives.
The European Union is ready to engage with Taliban but the Islamist group must respect human rights, including those of women, and not let Afghanistan again become a base for terrorism, the EU foreign policy chief said on Friday.
The US administration has no plans to release billions in Afghan gold, investments and foreign currency reserves parked in the United States that it froze after the Taliban's takeover.
