Aaron Swartz, 26, hanged himself in his flat weeks before he was to go on trial on accusations that he stole millions of articles from an electronic archive to make them freely available. If convicted he faced decades in prison and a fortune in fines.
He was pronounced dead on Saturday at his home in Brooklyn's Crown Heights neighbourhood, said Ellen Borakove, spokeswoman for New York's chief medical examiner.
Swartz was "an extraordinary hacker and activist", the Electronic Frontier Foundation, an international non-profit digital rights group based in California, wrote in a tribute. He "did more than almost anyone to make the internet a thriving ecosystem for open knowledge, and to keep it that way".
Among internet gurus, Swartz was considered a pioneer of efforts to make online information freely available.
"Playing Mozart's Requiem in honour of a brave and brilliant man," tweeted Carl Malamud, an internet public domain advocate who believes in free access to legally obtained files.
Swartz helped Mr Malamud's own effort to post Federal Court documents for free online, rather than the few cents per page that the government charges through its electronic archive, PACER.
In 2008, The New York Times reported, Swartz wrote a program to legally download the files using free access via public libraries. About 20 per cent of all the court papers were made available until the government shut down the library access. The FBI investigated, but did not charge Swartz, he reported on his own website.
Three years later Swartz was charged with stealing millions of articles from a computer archive at the Massachusetts Institute of Technology. Prosecutors said he broke into a computer wiring cupboard on campus and used his laptop for the downloads.
Experts were puzzled over the arrest and argued that the result of the actions Swartz was accused of was the same as his PACER program: information publicly available.
Swartz pleaded not guilty to charges including wire fraud. His trial was to begin next month.
According to a federal indictment, Swartz stole the documents from JSTOR, a subscription service used by MIT that offers copies of articles from academic journals. Prosecutors said he intended to distribute the articles on file-sharing websites.
He faced 13 felony charges, including breaching site terms and intending to share downloaded files through peer-to-peer networks, computer fraud, wire fraud, obtaining information from a protected computer and criminal forfeiture.
JSTOR did not press charges once it reclaimed the articles from Swartz, and some legal experts considered the case unfounded, saying that MIT allows guests access to the articles and Swartz, a fellow at Harvard's Safra Center for Ethics, was a guest.
Criticising the government's efforts to prosecute Swartz, Harvard law professor and Safra Centre faculty director Lawrence Lessig called himself a friend of Swartz's and wrote that “we need a better sense of justice ... The question this government needs to answer is why it was so necessary that Aaron Swartz be labeled a 'felon'."
JSTOR announced last week that it would make “more than 4.5 million articles” publicly available for free.
