Rally stages will be set up across the capital at 20 major intersections to disrupt the work of government officials and paralyse Bangkok, he said.
"Protesters from other provinces who miss the chance to join the main stage on Jan 12 can go to any other stages they want on Jan 13," he said.
The People's Democratic Reform Committee leader said he would take to stage at other sites on Jan 13, with details to be announced later.
Friday's announcement represents a change of plans, as Mr Suthep said earlier that Ratchadamnoen would be the main stage for the Jan 13 events.
The anti-government protest rallies began at Samsen railway station on Oct 31 after the House of Representatives passed the blanket amnesty bill, which was later killed by the Senate.
The rallies grew to include hundreds of thousands of people at some points, and Prime Minister Yingluck Shinawatra responded by dissolving the House and calling an election for Feb 2.
However, the protesters want the Yingluck government to step aside completely in favour of an appointed "people's council" to reform the country before any election is held.