The 38-year-old from Borås, in western Sweden, received a three-year prison sentence for the assault which was, according to prosecutors, the culmination of a prolonged campaign of physical and mental abuse against the woman and her daughter, his former wife.
The man had been attempting to defraud the Borås city council by claiming that he had been working as his mother-in-law's personal assistant.
He had forced her to falsify time sheets and allegedly coerced his wife into going along with the plan.
However a row broke out, during which the man kicked his mother-in-law in the chest.
She died from subsequent injuries, which included broken ribs and chest bones.
The prosecutor argued that as the man knew he was capable of killing the 60-year-old with such a powerful kick, he should face a murder charge.
Instead he was acquitted of murder and instead convicted of the lesser charges of aggravated assault and involuntary manslaughter.
The outcome of the case was slammed by the chief prosecutor Sven Urban Kvist, who had been pressing for a sentence of at least 10 years.
“I am not satisfied with the sentence. He was only convicted of aggravated assault and it should have been considerably longer than three years,” he told local newspaper Borås Tidning.
In addition to the charge against his mother-in-law, the man was also convicted of assaulting his ex-wife and her sister and was ordered to pay them damages of 180,000 kronor ($26,000).