According to Welby, he believed wrongly that an appropriate resolution would follow when he was told in 2013 that Smyth had been reported to the police.
Justin Welby has resigned as the Archbishop of Canterbury.
He announced his resignation in a statement.
This comes after the independent Makin review discovered that the Church of England covered up s3xual abuse by a barrister.
Following calls for his resignation, Welby said the report 鈥渆xposed the long-maintained conspiracy of silence about the heinous abuses of John Smyth鈥�.
According to Welby, he believed wrongly that an appropriate resolution would follow when he was told in 2013 that Smyth had been reported to the police.
In a statement, Welby said: 鈥�Having sought the gracious permission of His Majesty The King, I have decided to resign as Archbishop of Canterbury.
鈥淚t is very clear that I must take personal and institutional responsibility for the long and retraumatizing period between 2013 and 2024鈥�.
The independent Makin review into John Smyth QC鈥檚 abuse of children and young men was published last week.
John Smyth QC is said to have subjected his victims to traumatic physical, s3xual, psychological and spiritual attacks.
The report concluded he might have been brought to justice had Mr Welby formally reported it to police a decade ago.
Smyth died aged 75 in Cape Town in 2018 while under investigation by Hampshire Police, and so was 鈥渘ever brought to justice for the abuse鈥�, the review said.