Bonner, who was 88, died of heart failure Saturday afternoon in Boston, according to her daughter, Tatiana Yankelevich.
Bonner grew famous through her marriage to Sakharov, the Soviet Union's leading dissident, but she carved out her own reputation as a tireless human rights campaigner in the face of relentless hostility from Soviet authorities.
Bonner and Sakharov's cramped, three-room apartment in Moscow was the unofficial headquarters of the Soviet dissident movement in the 1970s, and again in the late 1980s after they returned from internal exile in the city of Gorky.
Both suffered constant harassment, and Soviet officialdom regularly made caustic, personal attacks against Bonner, accusing her of being a foreign agent who bullied her husband, the father of the Soviet atomic bomb, into turning against his country. But the attacks only seemed to strengthen their resolve, and neither ever stopped calling for greater personal freedom for Soviet citizens.
"I hope to live out my life until the end worthy of the Russian culture in which I've spent my life, of the Jewish and Armenian nationalities, and I am proud that mine has been the difficult lot and happy fate to be the wife and friend of academic Andrei Dmitrievich Sakharov," Bonner wrote in her autobiography.
After Sakharov died in 1989, and the Soviet Union collapsed two years later, Bonner continued to champion human rights, but was less and less visible, and her health began to deteriorate. She had a long history of heart and eye problems.
Nonetheless, she edited her husband's memoirs and still occasionally spoke out against President Boris Yeltsin's government, denouncing Russia's bungled war in Chechnya and the shortcomings of the country's young democracy.
In recent years, Bonner lent the weight of her voice to those opposing the leadership of Vladimir Putin, a former KGB officer who has restored many of the Soviet-era powers of the security services. In March 2010, hers was the first signature on a petition calling for Putin to go.
In December 2010, she sent a moving speech that was read at an opposition rally in Moscow in which she asks to be considered among those on the square: "Consider that I have come, again to save my homeland, although I cannot walk."
Bonner's remains will be cremated and eventually buried in a Moscow cemetery alongside her husband, mother and brothers, Yankelevich said. -- AP