Marc McKinlay, 38, assaulted Donald Maguire, 58, at Haymarket station on February 20, 2020.
Mr Maguire died from his injuries at the Western General Hospital in Edinburgh on March 4, 2020.
The High Court in Edinburgh heard McKinlay pushed Mr Maguire on his body which caused him to fall and hit his head off the ground. McKinlay then kicked Mr Maguire's son Brian on the body before striking him on the head with a bag containing cans of alcohol.
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McKinlay, of Cowdenbeath, Fife, was arrested after getting on a train.
He was found guilty of culpable homicide at the end of a four-day trial and had admitted assaulting Brian Maguire to his "severe injury".
During proceedings, the court heard that Mr Maguire and his son had been enjoying a night out in Edinburgh and had both gone to Haymarket station to catch a train back home.
Eyewitnesses said the Maguires came into contact with McKinlay, who was also there to catch a train. One witness said she thought McKinlay was drunk.
Architect Hugo Target, 35, told prosecutor David McLean that he was commuting home to Fife when he witnessed the incident.
He said he saw Mr Maguire fall backwards and that he landed on his back and "bashed his head". He then said he saw Mr McKinlay strike Brian.
Mr Target added: "Following that, I saw the man carrying the plastic bag swing his arm with the plastic bag and it hit the son on the face.
"There was some punches after that. I helped to separate them. I said something along the lines of, 'That's enough'; and I pulled the man with the plastic bag off the son.
"He then went downstairs and got on a train - it was the same train that I got on. Two officers then came on and took him off it."
Personal assistant Katie McCulloch, 40, witnessed the incident involving Mr Maguire and his son.
She told Mr McLean: "I remember feeling quite frightened. He was carrying some beers. I thought he was drunk. He was swearing. He was saying, 'Oh for f**k's sake, he's a f*****g a******e'.
"I backed away as he swayed onto the platform."
Ms McCulloch also told the court about McKinlay's attitude when police officers told him to get off the train.
She said: "I remember him pointing back towards his beers. He seemed to be more concerned about his beers than what happening on the stairs."
Travel agency worker Connie Dalrymple, 29, told Mr McLean that she saw a "bit of a fight".
She said she and her partner gave Mr Maguire CPR and she phoned 999.
Trial judge Fiona Tait told McKinlay that jail was the only option available to her.
She said: “I have read victim impact statements from Mr Maguire’s wife, son and daughter and these each describe in moving terms the understandable loss that Mr Maguire’s death has had upon them.
“There is no sentence which the court can impose that can bring Mr Maguire back to his family or indeed reflect his loss."
Judge Tait also gave McKinlay 15 months for assaulting Brian Maguire.