It comes after paediatric pathologist Dr Caroline Gannon resigned over interventions by Mr Larkin on abortion laws surrounding fatal foetal abnormality.
The Foyle MLA said the attorney general was supposed to be above politics.
"Mr Larkin's entitled to his own conscientious beliefs, religious and otherwise," Mr McCann said.
"Mr Larkin is not entitled, it seems to me, to go around the world, into European courts and so forth, expressing points of view which reflect his own moral religious beliefs, but which cannot be represented as the beliefs of the majority of people in the north.
"I think he's gone too far so I think he should leave."
Dr Gannon investigated the deaths of babies including those in the womb or stillbirths.
She said the recent interventions by Mr Larkin made her position untenable.
She said the final straw for her was having to advise a couple to use a picnic cooler bag to return their baby's remains to NI following an abortion in England.
A family can have a post-mortem examination carried out in England - but they are difficult to arrange.
Dr Gannon's resignation leaves Northern Ireland with only one paediatric pathologist.
Both the attorney general and the Department of Justice are involved in legal proceedings which are looking at the current law.
Peter Lynas, from the Evangelical Alliance, said he could see no reason why Mr Larkin has been singled out.
"I don't hear any call for the justice minister to stand down," he said.
"John is upholding the law as he is supposed to do, so I'm not quite sure what the series of offences are. How has he overstepped the mark?
"The attorney general's role is to uphold the law as it is and he is joined in that appeal by the Department of Justice."
People before Profit MLA Eamonn McCann has called for Attorney General John Larkin to stand down.