The McLean, Va.-based firm said in a statement that it fired Snowden on Monday "for violations of the firm's code of ethics and firm policy." It said he had earned a salary of $122,000 a year.
The firm called Snowden's actions "shocking" and said he had been a Booz Allen employee for less than three months.
Snowden has identified himself as the person who leaked top-secret information. He fled to Hong Kong in hopes of escaping criminal charges.
Booz Allen provides consulting services, technology support and analysis to U.S. government agencies and departments. Last year, 98 percent of the company's $5.9 billion in revenue came from U.S. government contracts. Three-fourths of its 25,000 employees hold government security clearances. Half the employees have top secret clearances.
Snowden previously worked for the CIA and likely obtained his security clearance there. But like others who leave the government to join private contractors, he was able to keep his clearance after he left and began working for outside firms.
Once given security clearance, workers can access offices, files and, most important, dedicated communications and computer networks that are walled off from the public.
Snowden says he accessed and downloaded the last of the documents that detailed the NSA surveillance program while working in an NSA office in Hawaii for Booz Allen.
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