Maulana Fazlur Rehman and his political party, Jamiat Ulema-e-Islam Fazl (JUI-F), one of the country's largest Islamist parties, is marching to Islamabad, calling for the removal of Prime Minister Imran Khan.
The ruling and the opposition parties have reached a deal to let the anti-government march progress as planned, provided that they protesters do not cross the sensitive "red zone" in Islamabad.
Fazlur Rehman is leading supporters from across Pakistan for days on a "Azadi March" towards Islamabad, with tens of thousands expected to come together in the capital.
"This movement will continue until the end of this government. There is no other way to bring Pakistan back on the democratic path," Rehman told reporters ahead of the march.
Rehman is set to arrive in Islamabad late Thursday, but until now has refused to clarify what happens next.
ILKHA