Mr Suthep and Nitithorn Lamlua, an adviser to the Network of Students and People for Reform of Thailand, asked the police and military commanders who guard Government House for permission to use the Santi Maitree building.
They plan to hold meetings of demonstration leaders and announce their daily statements there. In return, they promised to keep rank-and-file demonstrators outside the Government House complex.
The Santi Maitree building houses the offices of the prime minister and cabinet ministers.
Mr Suthep has threatened to take unilateral action as soon as Monday to set up a "people's government" if the Senate and courts fail to establish an interim administration as he has proposed.
The agreement was reached after Mr Suthep and Mr Nitithorn met with Col Sombat Thanyawan, deputy commander of the Cavalry Centre who supervises security at Government House.
After the meeting Col Sombat said the PDRC leaders were allowed to use the building to prevent the possibility of PDRC demonstrators breaking into Government House and causing damage. They could use only the Santi Maitree buiding, he said.
The Santi Maitree building is normally used as a venue for general events and ceremonies at Government House.