Bill Slagle, 44, of Cleveland was scheduled to be executed Wednesday for stabbing Mari Ann Pope 17 times while the children she was babysitting watched.
A spokeswoman for the Ohio Department of Rehabilitation and Correction said prison officials found Slagle hanging in his cell just after 5 a.m.
He was pronounced dead an hour later, The (Cleveland) Plain Dealer reported.
The spokeswoman, whose name was not reported, said the department was investigating the apparent suicide.
Slagle was denied clemency last month by Gov. John Kasich. Cuyahoga County Prosecutor Timothy J. McGinty had asked for the parole board to commute Slagle's sentence to life in prison, The Plain Dealer said.