Brendan Pallant, 37, faced a month-long trial in Victoria's Supreme Court after he pleaded not guilty to the 2019 murder.
On Monday, he was sentenced to 32 years imprisonment with a non-parole period of 25 years.
Jaidyn Gomes-Sebastiao, affectionately known as Snuffles, was just two-years-old when he died on September 2, 2019.
Pallant moved in with Jaidyn's mother, Stacie Saggers, 26 days before the child was found dead from head injuries in his bedroom at the Langwarrin home.
Ms Saggers, the mother of four boys, was introduced to Pallant by a friend after she moved back to Victoria from Queensland following the motorcycle death of her partner.
The pair moved in together within days, with Ms Saggers' two youngest children.
Jaidyn was described as an affectionate toddler but was also regarded as clingy and demanding of his mother's attention.
Ms Saggers called him a 'mummy's boy'.
Pallant was babysitting Jaidyn and his brother while the boys' mother was working, on September 2, when he fatally assaulted the toddler with a metal table in a "short burst of anger" because he couldn't see his own children.
Justice Jane Dixon said the 32-year sentence was higher than the standard punishment for murder, which is usually about 25 years.
"The fact the victim was a young and vulnerable child is a significant aggravating factor," she told the court.
"The life of an infant or a young child is especially precious because children are so vulnerable and defenceless.
"The ordinary natural instinct of any decent human being is to feel tenderness and protectiveness ... the offender's culpability in this case is of a high order."
Outside court, the boy's mother told reporters she and her family were "ecstatic" with "32 years of justice for Jaidyn".
With time served, Pallant could be eligible for parole by 2044.
He faced two trials. The first jury could not reach a verdict but the second found Pallant guilty of murder a year ago.