The execution of 71-year-old Edward Harold Schad Jr. came about two hours after the U.S. Supreme Court denied his final appeals.
He was given a lethal dose of pentobarbital at the state prison in Florence, and was pronounced dead at 10:12 a.m.
In his final hours, Schad thanked his lawyers and corrections officers who watched over him during the 35 days since his execution was scheduled, said Kelley Henry, a federal public defender who helped represent him.
"Ed Schad was a model inmate to the end," Henry said in a statement released by the defender's office in Phoenix.
Schad was sentenced to death for killing Lorimer "Leroy" Grove, whose body was found Aug. 9, 1978, in underbrush off the shoulder of U.S. 89 south of Prescott. A sash-like cord used to strangle Grove was still knotted around his neck.
Schad was arrested several weeks later in Utah while driving Grove's Cadillac. Authorities say he had driven the car across the country, used Grove's credit cards and forged a check from Grove's bank account.
At the time, Schad was on parole for second-degree murder in the 1968 strangulation death of a male sex partner in Utah. His lawyers in that case said the death was an accident.
Schad was convicted in Grove's death in 1979 and again in 1985 after the previous conviction was thrown out. The conviction was upheld by the state Supreme Court in 1989 but later became tied up in a series of federal court appeals.
The U.S. Supreme Court in June lifted a stay put in place by an appeals court, ordering the court to issue the execution authorization.
Schad always maintained he didn't kill Grove but told the state's clemency board at a hearing last week that he has accepted his fate.
A top Yavapai County prosecutor told the Arizona Board of Executive Clemency that despite Schad's denial, he was twice convicted by juries that rejected his assertion of innocence.
"He doesn't take any responsibility for what he did," chief deputy Dennis McGrane told the board. "Accidents two times, died of strangulation? I don't think so."
The board refused to recommend to Arizona Gov. Jan Brewer that Schad's sentenced be commuted to life in prison.
Schad's execution was Arizona's 35th since 1992. His death leaves 121 people on the death row in the state, including two women.