Taxi-driver Govindasamy Nallaiah was initially charged with the murder of Madam Low Foong Meng, the Chinese wife of his lawyer and childhood friend, Rengarajoo Rengasamy Balasamy, also of Indian-origin.
Govindasamy admitted to beating her unconscious with a bicycle chain and padlock at her husband's office, before setting the place on fire on August 10, 2011.
Mdm Low's charred body was found in the sixth-floor office at the Afro Asia Building.
An autopsy found the 55-year-old woman had died from smoke inhalation and extensive and severe burns. She had also sustained five skull fractures.
More From This Section
Govindasamy have been handed over a sentence of 10 years' without caning as his age is over 50 years, it said.
Judicial Commissioner Hoo Sheau Peng had called the difference "one of degree".
Govindasamy had known only that his actions would "likely" and not "probably" cause death, the Commissioner said.
But, she said, it had not been proven beyond reasonable doubt that Govindasamy's act "was so imminently dangerous that it would in all probability cause death".
Govindasamy's attack was "deplorable" and caused victim to suffer multiple injuries, said the Commissioner.
The court had heard during the trial last year that Govindasamy owed Rengarajoo Rengasamy Balasamy SGD 38,000 in legal fees incurred when the lawyer represented him in a 2002 corruption trial. He was given a deadline to pay up by August 10, 2011.
That morning, he went to Rengarajoo's office and tried to negotiate with Madam Low.
During his trial, Govindasamy told the court his actions stemmed from a "loss of control" after Mdm Low allegedly told him to "get lost" when he tried to negotiate legal fees he owed her husband.