Pimentel, 29, a Dominican native who converted to Islam and was to be tried in five days, was arrested in 2011 on charges of planning pipe bombings, and had already constructed one in the basement of an informant's home.
He pleaded guilty in State Supreme Court in Manhattan to a reduced charge of attempted criminal possession of a weapon as a crime of terrorism, the New York Times reported. He will be sentenced March 25 and faces up to 16 years in prison.
Pimentel faced life imprisonment under the original charges of weapons possession and conspiracy as crimes of terrorism.
The case in state court was unusual in that federal authorities, which typically handle terrorism prosecutions, chose not to pursue charges against Pimentel. The Manhattan district attorney, Cyrus Vance Jr., took the case instead, the Times noted.