Gordon Brown is the latest figure to warn against legalising assisted suicide after senior faith leaders staged an intervention on Wednesday.
Writing in The Times, the former Prime Minister said that legalising assisted suicide would "undermine the sanctity of life" and pose too great a risk to the vulnerable.
He also warned of a "slippery slope" towards the eventual "erosion" of safeguards and patient-doctor trust.
"If death were to become not just an option but something close to an entitlement through the bureaucratic processes that an Act of Parliament's provisions impose, we would, in my view, be altering fundamentally the way we think about mortality," he said.
"The risk of pressures, however subtle and indirect, on the frail and the vulnerable, who may feel their existence burdensome to others, cannot ever be entirely excluded.
"And the inevitable erosion of trust in the caring professions – if they were in a position to end life – would be to lose something very precious."
Brown has spoken out ahead of a second debate on Baroness Meacher's Assisted Dying Bill in the House of Lords on Friday.
The Bill would allow assisted suicide for the terminally ill who have been given less than six months to live, subject to the sign off of two doctors and a High Court judge. Critics have called the six month period arbitrary.
Brown's concerns are shared by faith leaders, with the Chief Rabbi, the Archbishop of Canterbury and head of the Roman Catholic Church in England and Wales coming together this week to urge Parliament not to change the law.
In a rare joint letter, they say that every life is a "precious gift" from God to be "upheld and protected", and that a compassionate society is one that should aim towards "assisted living rather than an acceptance of assisted suicide".
"All people of faith, and those of none, can share our concern that the common good is not served by policies or actions that would place very many vulnerable people in more vulnerable positions," they write.
"We appeal to people of whatever faith or belief to join us through our common bond of humanity in caring for the most vulnerable people within our society."
In a letter to Health Secretary Sajid Javid, over 1,700 doctors and nurses have spoken of their "great concern" about the proposals.
"The shift from preserving life to taking life is enormous and should not be minimised," they say.
