Michael Pearce has been sentenced to nine years in prison for killing six-week-old baby Alfie Sullock in Nelson.
The 33-year-old is likely to serve half of the sentence before being released on licence.
He was cleared of murder but found guilty of manslaughter by a majority verdict at Newport Crown Court yesterday, July 29.
Pearce killed the baby while his mother celebrated his birth on a “girly night out”.
He encouraged mum Donna Sullock, 29, to leave him alone with her child – saying “you can trust me”.
But a court was told during the trial how he attacked Alfie with bottles of bubble bath, baby power and hit him with a baseball boot.
Pearce tried to make out it was a tragic accident – calling paramedics who found Alfie “blue, cold and totally lifeless”.
Prosecutor Michael Mather-Lees had previously told the court: “Alfie was repeatedly beaten with objects and sustained gratuitous injuries.
“The baby was beaten with a shoe or sandal and the bottom of a plastic bottle.
“This was not a one-off moment of exasperation which can tragically happen with a screaming child.”
The magistrates son from Nelson was sentenced today, July 30, at the same court.