He died Wednesday at a Bakersfield hospital of complications from surgery, union spokeswoman Maria Machuca said.
"Richard understood that the struggle for a more perfect union and a better life for all America's workers didn't end with any particular victory or defeat, but instead required a commitment to getting up every single day to keep at it," President Barack Obama said in a statement.
Agriculture Secretary Tom Vilsack praised Chavez's dedication to ensuring that workers were treated with dignity and respect.
"Richard spent his life fighting for the rights of farmworkers -- some of the most vulnerable and hard working people in our society," Vilsack said in a written statement.
Born on the family homestead near Yuma, Ariz., the two brothers left farm work in 1949, spending a year working together in lumber mills in Northern California, Machuca said.
Eventually dedicating himself to union work, Richard Chavez organized the farmworkers' boycotts of California table grapes and other products in New York and Detroit during the 1960s and '70s. He was in charge of administrating union contracts in 1970, and later negotiated UFW agreements and oversaw union bargaining, Machuca said.
Chavez also designed the black Aztec eagle, the union's flag, and oversaw construction and helped build most of the major structures on the farmworkers' "Forty Acres" complex outside Delano, Calif. -- AP