The Royal College of Nursing (RCN) has dropped its opposition to the concept of helping patients to commit suicide.
The union has now adopted a neutral stance, neither supporting nor opposing a change in the law.
Health staff who provide patients with the drugs needed to kill themselves can face up to 14 years in prison.
The move comes as a survey for a newspaper suggests 74% of people want doctors to be able to help people to end their lives.
According to the survey of 1,500 people for the Times, support for assisted suicide was especially strong among those aged between 55 and 64.
The poll also suggests that six out of 10 people want friends and relatives to be able to help loved ones to die without fear of prosecution.
Dr Peter Carter, RCN chief executive, told BBC Radio 4 Today programme that assisted suicide was a complicated issue and that the nurses were split in their responses when consulted on the matter.
He said the shift to the neutral stance would allow nurses who were asked about it to engage in dialogue with patients but added: "That must not be confused with us being proponents of assisted suicide."
Calling for a Royal Commission, he said a public inquiry would help those confused about the law.
"If anyone assists someone to take their life they face up to 14 years in prison, but in reality no one has yet been prosecuted."
Members of the RCN council, which voted for the change on Friday, also decided that nurses should be given detailed guidance on the issue, which will now be drawn up.
The guidance will consider the complicated legal, regulatory, ethical and clinical frameworks around assisted suicide.
Dr Carter said this would ease the pressure on those nurses who felt by discussing assisted suicide, they could be interpreted as encouraging it.
The British Medical Association remains opposed to assisted suicide, having briefly and controversially adopted a neutral stance several years ago.
The RCN vote follows a three-month consultation of members, which drew over 1,200 individual responses.
Of those, 49% supported assisted suicide, but 40% were opposed to the concept.
Overall, the RCN represents 400,000 members.
Dr Carter said the consultation had shown that nurses placed great importance on the need to protect vulnerable patients, and to ensure adequate investment in end-of-life care
The Swiss organisation Dignitas has helped more than 115 people from the UK to commit suicide since it was founded in 1998.
The daughter of Ann Turner, a British doctor who died at the Dignitas building in Switzerland in 2006, said the RCN had made the right decision.
Sophie Pandit told BBC Radio 5 Live that her mother, who had a progressive and incurable degenerative disease called supranuclear palsy, had not wanted to suffer any longer.
The RCN decision follows unsuccessful attempts to amend the Coroners and Justice Bill, which sought to legalise aspects of assisting suicide, including travelling with those who wish to commit suicide abroad.
Dr Peter Saunders, campaign director of Care Not Killing Alliance, described the RCN move as a "quite bizarre" one which was based on a tiny percentage of its membership.
Sarah Wootton, chief executive of Dignity in Dying, which supports assisted suicide for the terminally ill, said the RCN was acting sensibly and the debate would continue for a long while yet.
Doctors at the BMA's annual conference in Liverpool this month voted overwhelmingly against supporting a motion "allowing the choice of an assisted death by patients who are terminally ill and who have mental capacity".
A BMA spokesperson said: "The BMA has a firm policy on this issue in that we are opposed to assisted dying and we are not lobbying for any change in the law in the UK."
Steve Fouch from Christian Nurses and Midwives (CNM) criticised the RCN's decision.
He said: "CNM does not feel the profession should step back from actively opposing legal changes that would loosen safeguards for vulnerable patients, or change the role of the nurse to one which actively aids the death of a patient.
"This would fundamentally change the nature of the nurse/patient relationship and would be detrimental to the care of dying, disabled, and elderly patients.
"At a time when there is growing anxiety about how we will care for the elderly and severely disabled in the future, this policy shift sends the wrong signals to the vulnerable."