William Garfield Bilbrough of Denton pleaded guilty to conspiring to transport and alien and to transporting an alien.
Bilbrough and a suspected co-conspirator, Brian Mark Lemley Jr. of Elkton, were accused of illegally bringing another member of The Base into the U.S.
Former Canadian Armed Services reservist Jordan Patrik Mathews, 27, is also charged in connection with plot.
According to prosecutors, in August, the pair drove from Maryland to Michigan to pick up another member of The Base who had fled Winnipeg, Canada.
The following month, the three of them participated in a training camp in Georgia hosted by another member of The Base.
At the session in Georgia, they bought hundreds of dollars worth of rounds and ammunition before returning to Maryland.
Bilbrough told prosecutors that the other two men took up residence in Delaware, and he visited there at least once.
During the visit, Bilbrough said he handled an assault rifle that had been constructed by the alleged illegal alien.
The trio discussed attending an upcoming pro-gun rally in Richmond, Va. and also about concocting a controlled substance, DMT.