Pinal County Deputies say James Sunderland abused his girlfriend's son. The baby was taken to the hospital with brain swelling and internal bruising, he later died.
Sunderland was convicted of first degree murder and child abuse.
On Thursday he was sentenced to life in prison.
"I am proud to say that justice was served, it at least brings justice," said Pinal County Attorney Lando Voyles.
The boys mother Amber Query, pleaded guilty to child abuse and was sentenced to 2 1/2 years in prison, and lifetime probation.