Mr Welby claimed he did not learn the full extent of prolific abuser John Smyth’s actions until 2017, despite the review stating he could have reported Smyth sooner.
John Smyth, who died in 2018, was responsible for abusing as many as 130 boys and young men over five decades in the UK and Africa.
Mr Welby said that in 2013, he was aware of only one allegation against Smyth and was preoccupied with other major abuse cases within the Church.
He admitted to being “insufficiently persistent” in pursuing Smyth’s case, which he cited as a reason for his resignation, describing it as a profoundly lonely experience.