Slattery died at his home in the Tulsa area late Friday following “a series of debilitating strokes,” Vicar General Fr. Gary Kastl said in a statement from the diocese.
In 2002, amid a Catholic Church sex abuse scandal involving clergy, Slattery apologized for reinstating the Rev. Kenneth Lewis in 1995 following allegations against him.
Slattery said at the time that when allegations emerged in 1994, Lewis was initially removed from the ministry but was reinstated after receiving psychiatric treatment.
“I have made mistakes along the way, and I feel terrible about it, but I do not feel guilty about it,” Slattery told the Tulsa World. “The mistakes are probably part of a culture of trying to protect the church.”
Lewis was later accused of sexually abusing a 13-year-old Oklahoma boy during a 2001 trip to Illinois.
Lewis was removed from the ministry and resigned in 2007. He eventually pleaded guilty to one count of sex abuse.
In 2009, the Tulsa Diocese was found out of compliance with standards set by U.S. Catholic bishops following the clergy sexual abuse scandal, but by 2010 had implemented training and other abuse prevention programs.
Slattery was also among the bishops who objected to the University of Notre Dame’s invitation to then-President Barack Obama to speak at its 2009 graduation ceremony and to present him with an honorary doctorate.
Slattery was born in Chicago and was ordained a priest in 1966. He was ordained as bishop in 1994 and shortly afterward installed as bishop of the diocese in Tulsa.
He oversaw an expansion of Catholic Charities of Eastern Oklahoma and creation of a new campus for the charity in north Tulsa as well as creation of a tuition assistance fund for Catholic families.
He resigned in 2016 after reaching his 75th birthday, as required under church law.
Slattery is survived by four sisters and one brother.