Mr. Browder’s lobbying took on a force in 2009, when Sergei L. Magnitsky, a tax lawyer for his company, Hermitage Capital, died in a Moscow prison, where he had been held for more than a year.
Mr. Browder turned the lawyer’s death into an international cause and succeeded in persuading Congress to pass a 2012 law, the Magnitsky Act, that barred Russian officials linked with his death from entering the United States or using its banking system.
The European Parliament later passed its own version of the act.
Mr. Browder was born in the United States but later renounced his American citizenship and became a citizen of Britain.
His grandfather Earl Browder was the head of the American Communist Party. His father became a mathematics professor at the University of Chicago, and his brother, Thomas, is an eminent particle physicist.