Sosa was best known for signature tunes such as "Gracias a la Vida" ("Thanks to Life") and "Si se Calla el Cantor" ("If the Singer is Silenced"). She had been in the hospital for more than two weeks with liver problems and had since been suffering from progressive kidney failure and cardiac arrest.
Her latest album, "Cantora 1," is nominated for three prizes in next month's Latin Grammy awards in Las Vegas, including album of the year and best folkloric album.
Affectionately dubbed "La Negra" or "The Black One" by fans for her mixed Indian and distant French ancestry, Sosa was born July 9, 1935, to a poor, working-class family in the sugarcane country of northwest Tucuman province.
Early on she felt the allure of popular traditions and became a teacher of folkloric dance.
At the age of 15, friends impressed by her talent encouraged Sosa to enter a local radio contest under the pseudonym "Gladys Osorio." She won a two-month contract with the broadcaster _ the first of many accolades over a career that continued until her final days.
"I didn't choose to sing for people," Sosa said in a recent interview on Argentine television. "Life chose me to sing."
By the 1970s she was recognized as one of the South American troubadours who gave rise to the "nuevo cancionero" (New Songbook) movement _ singers including Chile's Victor Jara and Violeta Parra, Argentina's Victor Heredia and Uruguay's Alfredo Zitarrosa who mixed leftist politics with poetic musings critical of the ruling juntas and their iron-fisted curtailment of civil liberties and human rights abuses.
In 1972, Sosa released the socially and politically charged album "Hasta la Victoria" ("Till Victory"). Her sympathies with communist movements and support for leftist parties attracted close scrutiny and censorship at a time when blending politics with music was a dangerous occupation _ Jara was tortured and shot to death by soldiers following Chile's 1973 military coup.
In 1979, a year after being widowed from her second husband, Sosa was detained along with an entire audience of about 200 students while singing in La Plata, a university city hit hard by military rule.
"I remember when they took me prisoner," she told The Associated Press in late 2007. "I was singing for university kids who were in the last year of veterinary school. It wasn't political."
She walked free 18 hours later under international pressure and after paying a $1,000 fine, but was forced to leave her homeland.
"I knew I had to leave," Sosa told the AP. "I was being threatened by the Triple A (a right-wing death squad that terrorized suspected dissidents during the 1976-83 military junta). The people from the navy, the secret services were following me."
With three suitcases and a handbag she headed to Spain, then France, becoming a wandering minstrel. Her pianist and musical director, Popi Spatocco, said exile was exceedingly harsh for a woman who loved Argentina.
Sosa returned home to wide acclaim in 1982 in the final months of the dictatorship, which she would ultimately outlive by a quarter-century.
The following year she released the eponymous album "Mercedes Sosa," which contained several tracks considered among her greatest hits: "Un Son para Portinari" and "Maria Maria"; along with "Inconsciente Colectivo" by Charly Garcia; "La Maza" and "Unicornio" by Silvio Rodriguez; "Corazon Maldito" by Violeta Parra; and "Me Yoy pa'l Mollar," together with Margarita Palacios.
Late in life, with South America's military regimes consigned to the dustbin of history, Sosa remained relevant by tapping powerful, universal emotions, singing about stopping war and ending poverty, about findng love and losing loved ones.
"There's no better example of artistic honesty," her nephew and fellow singer Chucho Sosa said in 2007. "Her songs reflects how she is in life."
Sosa won Latin Grammy Awards for Best Folk Album for "Misa Criolla" in 2000, "Acustico" in 2003 and "Corazon Libre" in 2006.
She also acted in films such as "El Santo de la Espada" ("The Knight of the Sword"), about Argentine independence hero Gen. Jose de San Martin.
Early this decade she took a two-year hiatus to recover from a series of falls _ one of which, she said, nearly left her paralyzed.
Sosa returned to the stage in 2005 and performed in some of the most prestigous venues of Latin America, the U.S., Canada and Europe.
All told, Sosa recorded more than 70 albums; the latest, a double CD titled "Cantora 1" and "Cantora 2," is a collection of folkloric classics performed with contemporary Latin American and Spanish stars such as Shakira, Fito Paez, Julieta Venegas, Joaquin Sabina, Lila Downs and Calle 13.