Brazilian President Luiz Inácio Lula da Silva has decided to ban mining and limit commercial agriculture, creating six new indigenous reserves.
It covers about 620,000 hectares (1.5m acres) of land, including the vast Amazon rainforest.
Indigenous leaders welcomed the move but said more areas needed protection.
Lula, who took office in January, promised to reverse the policies of his far-right predecessor, Jair Bolsonaro, who encouraged indigenous mining.
Lula, who served as president from 2003 to 2010, signed off on a vigil on Friday as indigenous people from across the country gather in the capital, Brasilia.
“We will legalize indigenous land,” the 77-year-old leader told the crowd.
“I don’t want any tribal area to be left without boundaries during the government. That’s my promise to you.”
And in a tweet, Lula described the decision as an “important step”.
Deforestation in the Amazon rainforest has increased at an alarming rate in recent years.
The new reserves are located in central Brazil and in the northeast and south of Brazil.
A presidential decree grants indigenous peoples exclusive access to the reserve’s natural resources. All mining is prohibited, and there are strict regulations for commercial farming and logging.
Welcoming Lula’s decision, some tribal leaders said that his government had sworn in to recognize the 14 new territories.
During his tenure, Bolsonaro made it his mission to promote economic development in the Amazon.
He has repeatedly argued that by mining in indigenous areas, Brazil, which relies heavily on imported fertilizers, can secure its own potash reserves. That claim has been questioned by some experts.