He has suffered from breathing problems related to a decades-long smoking habit. His attorneys said he has required a walker, relied on a colostomy bag and needed breathing treatments four times a day.
Prison officials planned to bring him into the death chamber in a wheelchair and also provide him a wedge pillow on the gurney.
Campbell's attorneys had warned the inmate's death could become a spectacle because of his breathing problems and because an exam failed to find veins suitable for IV insertion.
They argued he was too ill to execute, and also should be spared because of the effects of a brutal childhood.
Campbell spent Wednesday morning praying and watching TV, said JoEllen Smith, a prisons spokeswoman.
The U.S. Supreme Court on Tuesday refused to stop the execution. Last week, Republican Gov. John Kasich denied Campbell's request for clemency.
Campbell arrived at the death house Tuesday at the Southern Ohio Correctional Facility in Lucasville, about 85 miles south of Columbus. In the afternoon he was calm, Smith said.
The brother, sister and uncle of Charles Dials, fatally shot by Campbell in 1997, were to witness the execution, the Department of Rehabilitation and Correction said. Four attorneys were to witness on behalf of Campbell.
Campbell's last meal, called a special meal in Ohio, includes pork chops, greens, sweet potato pie, mashed potatoes and gravy, macaroni and cheese and milk.
He has chronic obstructive pulmonary disorder as the result of a decadeslong two-pack-a-day smoking habit, a prisons doctor has said.
Earlier this month, Campbell lost a bid to be executed by firing squad after a federal judge questioned whether lawmakers would enact the bill needed to allow the method.
Franklin County prosecutor Ron O'Brien called Campbell "the poster child for the death penalty."
Prosecutors said his health claims are ironic given he faked paralysis to escape court custody the day of the fatal carjacking.
On April 2, 1997, Campbell was in a wheelchair when he overpowered a Franklin County sheriff's deputy on the way to a court hearing on several armed robbery charges, records show.
Campbell took the deputy's gun, carjacked the 18-year-old Dials and drove around with him for several hours before shooting him twice in the head as Dials crouched in the footwell of his own truck, according to court records.
Campbell was regularly beaten, sexually abused and tortured as a child, his attorneys have argued in court filings and before the Ohio Parole Board.