Darren Murphy smashed John Morrison (50) in the face during an unprovoked attack in Glasgow city centre last December.
Mr Morrison – who had been enjoying a works night out shortly before the assault – died almost instantly after striking his head on the ground.
Bank worker Murphy left his stricken victim in the street – to go to a nightclub with friends.
Murphy told a trial last year that he had been acting in self defence – against a man who was almost a foot smaller and double his age.
But, it emerged yesterday the 26-year-old made-up the claims in a bid to trick the jury.
Murphy was back in the dock after earlier being convicted of culpable homicide.
Judge Norman Ritchie QC told him: “Fatefully John Morrison’s journey home that night crossed the route taken by you and your friends.
“It is not entirely clear what caused the altercation, but it is pretty certain it was not much.”
The judge said the decision to confront his victim was “without proper reason”.
Murphy looked ashen-faced as he was lead handcuffed to the cells. Many of his friends and family broke down in tears.
Mr Morrison – the former Lib-Dem leader of East Dunbartonshire Council – was attacked in the early hours of December 22 last year.
The lawyer had earlier been on a festive night out with colleagues from Glasgow City Council, where he worked as a legal manager.
His friend and work-mate Jennifer McMartin told the jury: “He was in really good form that night.
“He said he was in a good place in his life both professionally and personally having met his partner David.”
The court was shown CCTV of footage of Mr Morrison later in the city’s Argyle Street close to the St Enoch Centre.
Murphy and his friends were on the same street heading to the Arches Nightclub.
Pal Samantha Mulgrew claimed during the trial that Mr Morrison, of Milngavie, suddenly appeared next to her mumbling, which gave her a “fright”.
For some reason, Murphy and his group then turned on the solictor.
CCTV showed the booze-fuelled mob heading towards him before one pushed Mr Morrison as he appeared to be walking away.
Seconds later – and out of shot – six-foot one Murphy then pole-axed Mr Morrison by punching him in the face.
But, instead of checking how the dad-of-one was, Murphy carried on to the nightclub.
Mr Morrison died in the street despite medics coming to his aid. The ferocity of the blow had also broken his eye socket and nose.
Murphy’s friend Miss Mulgrew later told police that he had landed a “proper punch” on the ex-council leader.
The court also heard Murphy demanded friend Graeme Thomson not to say to police he had punched the lawyer.
But, during the trial, Murphy, of the city’s Bridgeton, denied he had punched Mr Morrison – instead claiming he had “hit him with a palm” to get him away.
Murphy insisted he had “felt threatened” by Mr Morrison that night – who was just over five foot in height.
However, Murphy told social workers compiling a pre-sentencing report that he had “fabricated” his evidence.
The killer said he had not felt “scared” of Mr Morrison and that he had made it up as he was worried about being convicted and sent to jail.
It emerged last month that Murphy was sunning himself in Ibiza awaiting trial – while his victim’s relatives continued to grieve back home.
Murphy – who had been on bail – told the jury that he had “thought about nothing else” since the killing.
But, photos plastered across his Facebook page showed the killer to be anything but heartbroken.
Murphy was seen jollying it up with friends this summer in Ibiza while later snaps showed him celebrating his birthday.
He made a self-pitying rant on Facebook just hours before he was sentenced yesterday blaming the media for depicting him as a “thug”.
Murphy claimed what happened was a “fluke” and that it “breaks his heart” he will not see his family for “a very long time”.
He went on: “I can choose to let it define me, confine me, refine me, outshine me or I can choose to move on and leave it behind me.
However, a source close to the case said: “He’s lucky he will meet his relatives again – those close to John Morrison are not so fortunate.”