Anthony Hayne, of Cleveland, apologized in court for his actions. He had pleaded guilty in a plea deal seeking to avoid a possible life sentence.
Three co-defendants pleaded guilty later but without plea deals. They were sentenced previously to eight- to 11-year terms.
A fifth defendant is undergoing a psychiatric exam.
The men were among five arrested in an FBI sting operation targeting a highway bridge over the Cuyahoga Valley National Park between Cleveland and Akron. The FBI has said the public was never in danger and the device was a dud provided by an informant.
The suspects were described by the government as self-proclaimed anarchists who acted out of anger against corporate America and the government. The defense has called the investigation a case of entrapment, with the informant guiding the way.