Sam Whittet, 22, of Knuston Spinney, had been drinking at the Brafield-On-The-Green Working Men’s Club in December last year when he punched Peter Roberts, 54.
Whittet threw a single punch at Mr Roberts, which knocked him to the ground.
He sustained a fracture to the base of the skull and a bleed to the brain.
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He has since remained in a life-threatening condition in a minimally conscious state and will require full-time care for the rest of his life.
Whittet pleaded guilty to GBH and to two counts of assault, which included an assault on a police officer where he headbutted the officer in the face while in a police cell.
At Northampton Crown Court on Friday, he was jailed for a total of two years and nine months.
When interviewed by police, Whittet claimed that he had no recollection of the assaults.
DC Lydia Watters, who led the investigation, said: “This has been a sensitive and emotional case, involving a number of people from a tight-knit community.
“The overriding factor has always been the concerns for the victim and his family.
“This incident highlights how extreme the consequences can be from a single punch, which has changed the lives of both the victim and offender in this case.”