Richard Rojem, 66, was pronounced dead at 10:16 am (1516 GMT), the Department of Corrections said in a statement, making him the second person the central US state has executed this year.
Rojem was sentenced to death after being found guilty of the July 1984 murder of seven-year-old Layla Cummings, who was the daughter of Rojem's ex-wife.
Cummings was abducted late at night between July 6-7 while her mother was at work, with her body found the next morning in a field.
A medical examiner testified that her body showed signs of rape and that she had died of multiple stab wounds to the neck region, court documents show.
On July 7, investigators found a beer cup with Rojem's fingerprint on it outside the Cummings' home, and a search of his house turned up a used condom with the same wrapper as that found in the field near the girl's body.
Rojem, then 26, had previously served time in prison for multiple sex offenses.
In addition to his death sentence for murder, Rojem was sentenced to multiple 1,000-year prison sentences for kidnapping and rape.
He maintained his innocence throughout his decades-long appeals process.
Rojem's execution, the ninth so far this year in the United States, came a day after another convicted rapist and murderer was killed by lethal injection in Texas.
The United States carried out 24 executions in 2023, all by lethal injection.
The death penalty has been abolished in 23 of the 50 U.S. states. Six other states -- Arizona, California, Ohio, Oregon, Pennsylvania and Tennessee -- observe a moratorium on executions.
Oklahoma resumed capital executions in 2021 after a six-year moratorium due to botched executions in 2014 and 2015.