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."

Team Sky's Gianni Moscon is facing disciplinary action from Team Sky after it emerged he used racially abusive language towards FDJ's Kevin Reza at the end of Friday's stage three.
Italian Moscon apologised and rode in Sunday's final stage.
"Any complaint will be investigated," the UCI told BBC Sport.
Team Sky chose not to withdraw Moscon from the race following discussions with FDJ. Moscon has apologised to Frenchman Reza and his team-mates but the British team will consider what action to take after establishing all of the facts of the incident.
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The three-week trial on the 23.4m long 'up' escalator at Holborn station is taking place during peak hours.
Transport for London said the move will "increase the capacity" and prevent "queuing at the bottom" as people stand on both sides of the escalator.
More than 56 million passengers use the station every year.
Usually passengers stand to the right, leaving the left side free for people to walk up or down the escalators.
Holborn Tube station, one of the busiest on the network, is set to get a new entrance and an enlarged ticket hall in order to increase its capacity by 80% by 2022.
Peter McNaught, operations director for the Central line, said: "In the meantime, as part of a three-week trial to reduce queues and keep people moving through the station, we are encouraging customers to stand on both sides of the 'up' escalators during busy periods.
"We believe this will increase the capacity of the escalators as more people will be able to board, preventing queuing at the bottom of the escalator."
People before Profit MLA Eamonn McCann has called for Attorney General John Larkin to stand down.
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Cycling's governing body has warned that any rider found guilty of racism will be sanctioned after an incident during the Tour de Romandie.
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Commuters are being asked to stand rather than walk on the left side of escalators at a central London Tube station to see if it can cut queues.