Shaun W. Bridges, 33, of Laurel, Maryland, must also forfeit US$650,000, the U.S. Justice Department said.
Bridges pleaded guilty on Oct. 31 in the U.S. District Court for the Northern District of California to money laundering and obstruction of justice.
He was one of two federal investigators charged with crimes committed during the probe of the Silk Road, which was shut down in October 2013.
Ross Ulbricht, who was accused of being the site's operator, was sentenced to two concurrent life sentences and 40 years in prison. He is appealing.
Bridges had been a special agent with the Secret Service's Baltimore Field Office. He admitted using an administrator account on the Silk Road website to transfer 20,000 bitcoins into his own account in early 2013.
When the bitcoins appreciated, he sold them and deposited $820,000 into personal investment accounts, according to prosecutors.
The second corrupt investigator, former DEA agent Carl Mark Force IV, pleaded guilty in July to money laundering, obstruction of justice and extortion under color of official right.
Prosecutors alleged he used his position to illegally garner $700,000 worth of bitcoins during the course of the Silk Road investigation. He was sentenced in October to 78 months in prison.