The former minister branded the 44-month term handed to John Broadhurst as 'unduly lenient' and said she was 'horrified' by the decision.
Broadhurst, aged 40, was jailed after admitting the manslaughter of Natalie Connolly, who he left bleeding to death at the bottom of their stairs at the Kinver home after a 'rough sex session'.
He had previously been on trial for murder, before the charge was reduced.
Ms Harman, a former solicitor general and ex-acting Labour leader, said the sentence 'could not be allowed to stand' as she urged Attorney General Geoffrey Cox to examine the case.
She insisted the charge should have stayed at murder.
Ms Harman said: “Bearing in mind she died of violent injuries inflicted on her by him it’s hard to see how the sentence wasn’t even four years.
“This is a very ominous development.
"We stopped men getting away with murder by blaming their wife’s infidelity and now we’ve got a new version of male justification for homicide.”
The trial heard how Broadhurst told 999 operators he had woken to find Miss Connolly 'dead as a doughnut' at their Kenrose Mill home in December 2016.
The couple had spent the previous day drinking with friends while watching a West Bromwich Albion game at The Hawthorns before going for a curry and returning home for their consensual 'rough sex' session.
More than 40 injuries
The mother-of-one was discovered the following morning with more than 40 injuries, including serious internal trauma, and was more than five times the drink-drive limit.
A post mortem showed the 26-year-old died from acute alcohol intoxication and blunt force injuries.
After Broadhurst was sentenced, Miss Connolly's family described him as 'callous and disrespectful'.
"It is now clear to us that the guilty admission made by Broadhurst shows the heartless way in which he left Natalie at the bottom of the stairs, without any concern for her dignity or wellbeing," they said.
"Natalie was in the prime of her life and if Broadhurst had got the medical help from the emergency services at the time of this incident, Natalie may still be alive today."
Meanwhile Miss Connolly's 10-year-old daughter told the court: "I wanted to cry all day long. I miss her smile, her hugs, her kisses, saying 'I love you'. I will never forget her laugh.
"I believe mummy is an angel in Heaven. She will have a good and happy life in Heaven and no one will hurt her.
"I don't like people talking about mummies because I will never see mine again."