US Edition Gardner, 49, chose to die by firing squad - an option open to him because he was convicted before Utah adopted lethal injection in 2004.
He was strapped to a black metal chair surrounded by sandbags to stop ricochets.
A white target was then pinned over his heart, a hood placed over his head, and five volunteer marksmen armed with .30-caliber rifles opened fire from behind a wall.
Only four of the weapons were loaded with live rounds and one contained a wax bullet, allowing the marksmen to retain some doubt over whether they fired the fatal shot. He was pronounced dead at 12:17 am. The executioners were all certified police officers who remain anonymous. They stood about 25 feet from Gardner.
Asked if he had any last words, Gardner replied: "I do not. No."
Gardner was served his last meal on Tuesday having decided to fast for 48 hours. It consisted of steak, lobster, apple pie, vanilla ice cream and 7-Up.
He spent his final hours watching the Lord of the Rings film trilogy and was said to be “relaxed.”
Shortly before the execution his lawyer Andrew Parnes said: “He's just really strong. Now is that bravado? I don't know.”
Gardner asked that none of his relatives attend the execution and they gathered outside Utah State Prison.
His brother Randy said: “He didn't want nobody to see him get shot. I would have liked to be there for him. I love him to death. He's my little brother.”
Utah Governor Gary Herbert denied his request for a temporary stay of execution, saying Gardner had already received “a full and fair opportunity” to have his case considered.
Gardner and his defense attorneys fought to stop the execution to the end. They filed petitions with state and federal courts, asked a Utah parole board to commute his sentence to life in prison without parole, and finally unsuccessfully appealed to Utah Gov. Gary Herbert and the U.S. Supreme Court.
Gardner even tried to appeal to the general public, setting up an interview with CNN's "Larry King Live." But the Utah Department of Corrections canceled the phone interview minutes before it was scheduled to take place Wednesday.
Gardner was the third man executed by firing squad in the US since a Supreme Court ruling reinstated capital punishment in 1976.
Utah altered its capital punishment law in 2004 to make lethal injection the usual method but Gardner, and eight other death row inmates convicted before that date, retained the right to choose a firing squad if they want.
Gardner's lawyer said his client’s decision to die by firing squad was not made from a desire to draw attention to his case, it was simply his preferred choice.
Gardner was sentenced to death for the murder of lawyer Michael Burdell during an escape attempt in 1985.
He had been trying to escape from a court where he was already facing another murder charge over the shooting of a barman.
Shortly before his execution he claimed to be a changed man, saying he wanted to start an organic farm project for youngsters.
He also argued that the passage of time since the crime meant it was unjustified to put him to death.
Before his conviction he had been addicted to hard drugs as a child, spent 18 months in a mental hospital and been sexually abused in a foster home.
The case has renewed debate about the use of the death penalty in the US and divided family and friends of his victims.
Burdell’s fiancée Donna Nu said the late lawyer would have opposed the execution.
Elisabeth Semel, director of the Death Penalty Clinic at the University of California, Berkeley, said: “It's difficult to understand the issue of how can we still be engaged in this form of barbarism.”
Utah Attorney General Mark Shurtleff announced to the world he had signed off on the execution via micro-blogging site Twitter.
"I just gave the go ahead to Corrections Director to proceed with Gardner's execution," Shurtleff tweeted shortly before Gardner was shot through the heart by a five-man firing squad at Utah State Prison.
"May God grant him the mercy he denied his victims."