Alexander Ciccolo's guilty plea comes a month before he was scheduled to go to trial. He faces 20 years in prison when he is sentenced in September.
Ciccolo was arrested in July 2015 after he received four guns he'd ordered from a person who was cooperating with the FBI. Boston police Capt. Robert Ciccolo tipped off authorities after his son said he wanted to join the Daesh.
Ciccolo, 25, was initially charged only with being a felon in possession of a firearm and stabbing a nurse in the head with a pen after he was brought to jail. But he was later indicted on attempting to provide material support to a foreign terrorist organization and attempting to use weapons of mass destruction.
Ciccolo, who went by the name Ali Al Amriki, pleaded guilty to all charges. His lawyer did not immediately respond to an email seeking comment.
Prosecutors say Ciccolo told the person cooperating with authorities that he planned to commit acts of terrorism to support Daesh, including attacking an unidentified university using assault rifles and homemade bombs similar to the pressure cooker bombs used in the deadly 2013 Boston Marathon attack. The bombing at the marathon finish line killed three people and injured more than 260 others.
Ciccolo was seen buying a pressure cooker shortly before his arrest, prosecutors said.
Prosecutors say agents found partially made "Molotov cocktails" in Ciccolo's apartment after he was arrested. Authorities say posts on Ciccolo's Facebook page included a photo of a dead American soldier that said "Thank you Daesh!"
Ciccolo's mother, Shelley MacInnes, told New England Public Radio last year that her son is "very compassionate" and "would not hurt a fly." He converted to Islam a few years ago, his mother said.