Jeremy Hammond, whose case has been supported by digital rights activists and others, also was part of a group which broke into the FBI computer network and later delivered documents to WikiLeaks, according to investigators.
He was sentenced by a US federal judge in New York after pleading guilty in May to conspiracy charges in connection with the 2011 hack of Stratfor, the US attorney's office said.
"As he admitted through his plea of guilty, Jeremy Hammond launched a series of computer hacks that stole confidential information pertaining to companies, law enforcement agencies, and thousands of innocent individuals," US Attorney Preet Bharara said in a statement.
Officials said Hammond and his co-conspirators stole confidential information, including Stratfor employees' emails as well as account information for approximately 860,000 Stratfor subscribers or clients.
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Officials also say the group stole credit card information from 60,000 credit card users and used that to make more than USD 700,000 in unauthorized charges.
His supporters claimed he was exposing wrongdoing, some comparing him to Chelsea Manning, the US army private prosecuted for giving some 700,000 classified diplomatic and military documents to WikiLeaks.
The Electronic Frontier Foundation argued in a brief that Hammond "did not profit financially as a result of his actions, but rather, exposed uncomfortable truths."
Hammond read a statement in court claiming his acts were "civil disobedience," according to the text released by his supporters.
"The acts of civil disobedience and direct action that I am being sentenced for today are in line with the principles of community and equality that have guided my life," the statement said.