"That is our position and ... I think this would be God's position too," Tutu said when questioned about the appropriateness of forgiving Breivik, who is serving an extendable 21-year prison sentence for killing 77 people in 2011.
"God hates no one. We are all God's children and there are those of us who become bad children but we're still children, we still belong to the family," he added during a press conference at the Oslo Nobel Peace Centre, 30 years after receiving the prestigious award.
The retired Anglican archbishop said that forgiveness is compatible with considering Breivik's crimes as "the worst possible thing that you could imagine", but highlighted that hatred and bitterness are "corrosive".
On July 22, 2011, Breivik killed eight people near a governmental building in Oslo with a bomb before going on to open fire at a Youth Labour camp on the island of Utoeya, where another 69 people died, most of them teenagers.
Trond Henry Blattmann, president of the support group for relatives of the victims and the father of one of the dead, said he was unable to forgive a criminal who had shown no remorse.
"We have here a mass murderer who doesn't show any remorse and will not change his personality," Blattmann told public broadcaster NRK.
"Quite the opposite, he says that he would have liked to take more lives and that he would gladly do it again."
Tutu, an anti-apartheid activist who later became the president of South Africa's Truth and Reconciliation Commission, was expected to meet Breivik's main lawyer, Geir Lippestad, in Oslo on Tuesday evening for a debate on reconciliation.