Leroy Smith III decided to change his plea just before opening arguments were slated to get underway.
Smith is accused of killing his father in 2014 and dismembering his body.
But authorities said he suffers from delusions and he became the first in Maine to be forced to take medication in order to make him competent to stand trial.
Smith had pleaded not guilty to murder and manslaughter and also entered a plea of not criminal responsible because of his mental state.
Our crew in Augusta said he decided to plead guilty to the lesser charge of manslaughter this morning.
He has been ordered to be housed at the Riverview Psychiatric Facility for an still undetermined amount of time.