"Peter was a friend, colleague and politically courageous champion of the downtrodden and mistreated of the entire Western Hemisphere," Nader wrote in a statement released Saturday. "Everyone who met Peter, talked to Peter, worked with Peter, or argued with Peter, will miss the passing of a great American."
Camejo ran for the state's top office in 2002, 2003 and 2006, supporting abortion rights, universal health care and a moratorium on the death penalty. Before joining the Green Party, he also ran for president as the Socialist Workers Party nominee in 1976.
During the 2004 presidential contest, Camejo was independent Nader's vice presidential pick.
Last month, Camejo, who lost his hair from chemotherapy, attended the Peace and Freedom Party convention in Sacramento to endorse Nader's current bid for the presidency with running mate Matt Gonzalez.
"Ralph Nader is more than a candidate, he's an issue," Camejo said in his Aug. 2 speech, adding that Nader brought true reform, offering an independent choice to the "ruling party."
Nader said Camejo passed away a few days after completing his autobiography, which has a working title of "Northstar."
According to a statement put out by Camejo's family on a blog that had been updating his condition, Camejo voluntarily returned home Friday after undergoing treatment at UC Davis Medical Center in Sacramento for a reoccurrence of lymphoma.
"Peter's health had declined rapidly over the last two days due to the aggressiveness of his cancer and the strength of the drugs used to combat his disease," according to the family statement. "His wife was at his side when he passed peacefully this morning."
The family is planning private funeral services, and a public memorial will be arranged later.