A jury at Derby Crown Court took two days to unanimously find him guilty of the murder of Andrew Jackson, following seven weeks of evidence.
High on cocaine and amphetamine, Smith inflicted 38 separate injuries using a knife and the butt of an air rifle, in a “sustained attack” at Mr Jackson's caravan home, on an allotment, off Prospect Drive, Shirebrook.
The 55-year-old managed to stagger outside but collapsed and died on the ground. His body was discovered at around 10am on Sunday, January 26, 2020.
Smith, now 28, of Alder Way, Shirebrook, denied a single count of murder, and appeared by video-link from prison on Wednesday.
He remained impassive throughout the hearing, but expressed his thanks, through his barrister, for the fair way his case had been heard.
On Wednesday, Judge Smith told him: “Clearly something happened outside that caravan in the early hours of that morning to cause you to do what you did. Only you know what it was.
"You didn’t intend to kill, but there was an intention to cause really serious harm. It started spontaneously – though it finished tragically.”
Mr Jackson was described as “a polite and friendly man,” who was eccentric, but well-liked by local residents.
"Even you said what a nice man he was,” Judge Smith told the defendant.
In a victim impact statement, Mr Jackson’s brother spoke of the “devastating impact” on their family, who had lost touch with him many years ago.
"I never got the chance to tell him he could come home and turn his life around,” he said. “We are struggling to come to terms with the way he died – gasping and struggling for breath in an allotment, on his own.”
He said it was a waste of two lives because Smith’s family would lose him during his imprisonment.
A pathologist said that Mr Jackson’s life could have been saved if only Smith realised what he had done and sought help.
The court heard Smith had only one previous conviction, and was deeply affected by the death of his father and the breakdown of his relationship at the time.