Welby admitted to "shameful" decisions not to act when he became aware of the abuse that had been going on for many years in the 1970s and 1980s, according to British media.
He apologized, but was met with a long list of demands for his resignation from high-ranking officials within the church, including bishops, and his situation eventually became untenable.
"It is very clear that I must take personal responsibility and institutional responsibility," Welby writes in a statement according to AP. He adds that he is doing it for the good of the church.
Over 100 victims
Over 130 boys are believed to have fallen victim to the abuse at church summer camps in the UK, Zimbabwe, and South Africa. The man accused of the abuse later became a well-known lawyer and is now deceased.
What makes it worse for Welby is that he worked as a volunteer at several of the camps where the abuse took place, according to himself without knowledge of the abuse or the allegations that emerged in the 1980s.
In 2013, Welby was informed about the suspected abuse and was also told that it was "unlikely" that he was unaware of the rumors that had spread about the accused 30 years earlier, when the accused was still alive.
Opened up to women
However, neither he nor other high-ranking officials within the church took action. In last week's report, it is stated that "their response was completely inadequate and in practice a cover-up".
The 68-year-old Welby became Archbishop of Canterbury in 2012 and during his tenure, the church has opened up to female bishops and allowing priests to bless same-sex couples.
His greatest tasks have been to deliver the sermon at Queen Elizabeth II's funeral and then to crown King Charles III.
