They demanded the government address their grievances.
The protesters, who have come together under a group called the People's Movement for a Just Society (Pmove), left Chiang Mai last Thursday with other compatriots joining up along the way until they arrived in Bangkok yesterday.
They are protesting against the government's sluggishness in solving the problems of landless farmers, displaced people, and those affected by more than 500 state projects and policies.
They also called on the government to speed up the issuance of community land deeds, a programme initiated by the previous Democrat government, and to press ahead with the Ban Mankhong housing projects for slum residents.
The rally also marked UN World Habitat Day yesterday.
Sawai Laolong, a 76-year-old slum dweller from Chonglom community in Bangkok's Yannawa district, said the community faced eviction by a private firm that owns the land plot where her community is located.
"I want to continue staying on this land where I have lived for over 30 years," she said. "I survive on a 700-baht old-age pension from the government and it is impossible for me to rent a house or buy this land."
Ms Sawai, who lives alone, said many slum residents were facing eviction like herself and she wanted Prime Minister Yingluck Shinawatra to solve the problem by securing the community's right to stay on the land.
Another demonstrator from Chiang Mai province, Direk Kong-ngaen, 52, said he faced three criminal charges and a civil case for trespassing after he farmed on a six-rai deserted land plot in the province. Mr Direk said he knew the land belonged to a private owner, but it had been left idle. He was poor and badly needed land to farm to make a living, he added.
The farmer said he had joined Pmove's campaigns to pressure previous governments but none had been willing to solve their problems.
"I was delighted when the Yingluck administration announced its policies to fix land rights problems, but in practice there has been no progress," he said.
The government set up a committee, chaired by former interior minister Yongyuth Wichaidit, to look into Pmove's petitions on Jan 15 this year, but the panel made no progress.
The group yesterday condemned the government for insincerity and lack of attention to their plight.
"We are here to negotiate with the prime minister once again to seek approaches to solving the problems," said Pongsak Saiwan, Pmove's co-ordinator.
Prayong Dok-lamyai, an adviser to Pmove, said the Yongyuth committee failed while the government had been attempting to revoke several measures initiated by the previous Democrat government _ such as community land title deeds and the Land Bank scheme, which could help solve land ownership disputes and the longstanding problems of landless people.
"We need to talk to the premier and want her to chair the committee herself," he said.
Mr Prayong said Ms Yingluck's team had informed the group that the prime minister will hold talks with 15 of its representatives at 9am today.
He said the group would continue to camp outside Government House if they are not satisfied with the outcome of the discussions.