During a meeting of the doctors union's annual representative meeting (ARM) in Dorset on Tuesday, they decided to back a motion stating that abortion should no longer be a criminal offence.
Dr Peter Saunders, Chief Executive of the Christian Medical Fellowship said: "This decision defies common sense and will dismay thousands of ordinary doctors and nurses with their unprecedented decision.
"What the BMA has chosen to do is back abortion on demand, without restriction including on length of gestation and sex."
A ComRes survery conducted last year found that the majority of women wanted to see tighter abortion laws and even a reduction in the current 24 week limit on terminations.
Peter Williams, a Christian and the executive officer for Right to Life, told Premier: "This is a terrible decision. I'm not quite sure the members of the ARM (annual representative meeting) really understood what they were getting into or actually voting for.
"It was something which was very poorly thought out and unfortunately what it will mean is the BMA campaigning for even more inhumane legislation."
The BMA said it believes controls should still restrict when abortions can be performed, however professional and regulatory - not criminal - sanctions should be enforced.
Dr John Chisholm, BMA medical ethics committee chair said: "Abortion is currently a crime, with exceptions, throughout the UK.
Following the debate, the majority of doctors were clear that abortion should be treated as a medical issue rather than a criminal one. What must be clear is that decriminalisation does not mean deregulation.
The body said its stance on broader issues concern when and how abortion should be available "remain unchanged". The BMA's motion did not include increasing the current 24 week limit on terminations.
Top picture: British Medical Association council chair Mark Porter