Darrell Ferguson, 28, the youngest person put to death in Ohio since 1962, died by injection at 10:21 a.m. at the Southern Ohio Correctional Facility.
He had asked for the death penalty and chose not to pursue appeals, which could have delayed his execution for years.
Ferguson was the second inmate executed using the state's new lethal injection protocol, adopted after an execution in May was delayed while prison staff struggled to find a useable vein on that inmate, who asked them to find another way to kill him.
Officials said Ferguson's veins were closely examined before his execution, and the guidelines called for two injection sites to be prepared plus a new method of ensuring veins stay open.
Ferguson was convicted of three counts of aggravated murder in the Christmas Day killing of Thomas King, 61, in 2001 and the deaths the next day of Arlie Fugate, 68, and his wife Mae, 69. King was disabled and used crutches, Arlie Fugate had cancer and Mae Fugate took meals to wheelchair-using neighbors.
The victims let Ferguson into their homes in Dayton because they knew him. Ferguson's mother had been married to King's brother, and Ferguson's family had once lived near the Fugates.
Ferguson committed the murders after getting a two-day pass from a drug treatment program he had been ordered to attend following a burglary conviction.
At his sentencing, he taunted the victims' families, saying he worshipped Satan, enjoyed the killings, had no remorse, and, if released from prison, would pick up where he left off.
Defense attorney Victor Hodge said Ferguson's behavior might have been a ploy to make sure he was sentenced to death so he could avoid spending the rest of his life in prison.