Michael McCarthy is guilty of second degree murder in the 2015 killing of Bella Bond, the child known as Baby Doe.
A jury deliberated over several days before convicting McCarthy yesterday.
The child's body was found in a garbage bag on Deer Island in June of 2015, then went unidentified for over two months.
McCarthy will be sentenced tomorrow, when he faces a mandatory sentence of life in prison with parole available after 15 years.
Meantime, his attorney Jonathan Shapiro called the jury verdict "a travesty of justice." He was most upset that the trial judge toward the end of the trial added a lesser charge of second degree murder which in the long run the jury opted for.
Shapiro said an appeal will be filed.