William Andrew O'Sullivan was last year jailed for nine years for manslaughter in a sentence the state government labelled "manifestly inadequate".
On Tuesday, the Queensland Court of Appeal increased his sentence to 12 years.
"This takes into account the seriousness of an offence that was constituted by the deliberate infliction of fatal violence by an adult male upon an infant in his care," the court said.
O'Sullivan, the partner of Mason's mother, fatally struck the 22-month-old in the abdomen and failed to get him medical treatment as he suffered an agonising death over five days.
"This young child was dealt with in a callous manner," Director of Public Prosecutions Michael Byrne QC told the appeal court in June.
"There was an unwillingness to provide any basic care and tenderness."
Mason's mother, Annemarree Louise Lee, also pleaded guilty to manslaughter for failing to get the boy medical treatment.
But the Court of Appeal has dismissed a bid to increase her nine-year sentence.
This story was first published on 7NEWS and has been republished here with permission.