|Morales has championed the rights of Bolivia's
indigenous peoples since entering office [AFP]
Morales's Movement Toward Socialism, or MAS party, had enough votes to ratify the bill in the lower house and senate, but the opposition had refused to grant the quorum needed for a vote.
MAS controls the lower chamber, but opposition parties have used their slim majority in the senate to block dozens of government-proposed reforms.
Morales's opponents say the law will give him political advantage because it assigns more seats to the poor, indigenous parts of the country whose rights he has championed since he took office in 2006.
However, a deal was reached after Morales ordered officials to compile a new electoral register, following opposition leaders' claims that he could exploit "flaws" in the existing census to rig the vote.
Morales had earlier condemned the opposition for being "racist, fascist, selfish" in refusing to ratify the law.
He also said that he had received supportive phone calls from Hugo Chavez, the Venezuela president, and Fidel Castro, the former president of Cuba.
Morales, a former coca farmer, has said he once went without food for 18 days in 1998 to protest against the then-government's policy on coca, the raw material for cocaine revered by Bolivian Indians for its medicinal and nutritional properties, Reuters reported.