An "unprecedented" 85 MPs are bidding to speak on historic backbench legislation which could enshrine the right to die in British law.
Labour MP Rob Marris warned Parliament must be at its best as it wrestles with the controversial Bill, which would allow adults of sound mind and with less than six months to live the right to ask for medical help to die.
He moved the Assisted Dying Bill in a packed House of Commons as the newly elected MPs faced their first key issue of conscience since the General Election.
At the start of the debate, Deputy Speaker Natascha Engel said the demand to speak from the backbenches meant MPs must keep remarks brief to allow as many into the debate as possible.
Mr Marris' Bill is facing passionate opposition ahead of what is likely to be the first vote on the issue in almost 20 years.
He told MPs: "I hope today we can see Parliament at is best, with an open debate and a free vote on a matter of conscience.
"The current law does not meet the needs of the terminally ill, does not meet the needs of their loved ones. And in some way it does not meet the needs of the medical profession.
"We have amateur suicides going on. We have what would be technically illegal assistance going on. We have those who have the means going off to Dignitas in Switzerland.
"The Supreme Court in the Tony Nicklinson case recognised there was a problem which needs to be addressed by Parliament.
"It is time Parliament grasped this issue."
Mr Marris' Bill must be voted on before 2.30pm to get a second reading and make progress in the legislative path towards the statute book.
As the debate began inside the Commons chamber, protesters outside Parliament urged MPs not to change the law.
But Mr Marris, the Wolverhampton South West MP, said social attitudes to the right to die had changed since the last Commons vote on the issue in 1997.
He told the Commons: "We all know as politicians not to rely too much on opinion polls - however, opinion polling by Dignity in Dying of 10,000 people, carried out independently by Populus, suggested extremely strong support for the kind of measure I am proposing to the House today.
"I respect the views held by people who are strongly opposed to my Bill. I share their motives for a better society and making sure we have a law which protects people.
"When I came in this morning on the Tube, I stood next to a man with a hoodie on saying on it 'understand difference'. I thought that was quite appropriate.
"This debate is not about opinion poll numbers. It's about conscience and ethics and the kind of society in which we live. We need the debate and Parliament should debate this issue."
Mr Marris' Bill faced immediate opposition. Liberal Democrat John Pugh asked why his Bill was not called the Assisted Suicide Bill, while Tory Fiona Bruce insisted he was misreading the Supreme Court view in the case of Mr Nicklinson.
Labour's Gisela Stuart demanded to know what a doctor was supposed to do if a patient handed fatal medication were to choke while they took it, while former Wales Secretary David Jones said it should have included guidance for the High Court judge who would be asked to sign off on any request to die.
Mr Marris said his Bill included many safeguards and a clear process.
Under the terms of the legislation, two doctors and a High Court judge would have to be satisfied of the requesting patient's eligibility - defined as being terminally ill with less than six months to live, mentally fit to make the decision and aware of alternatives - before the right to die would be allowed.
The patient would be given a 14 day cooling off period before the assistance to die would take place. The patient must administer the fatal medication themselves under the rules in the Bill.
Any doctor is allowed to exempt themselves from the process on conscience grounds.
But Labour's Helen Jones (Warrington North) said: "Your Bill is founded on the belief it is possible to predict the time of death up to six month accurately. In fact, most doctors will tell you that is impossible - certainly impossible to predict beyond a week or two. Is that not the case?"
Mr Marris said: "Professionals often give advice on a balance of probabilities. That is the same for medical professionals. In fact, on the gross statistics when errors in prognosis occur for the terminally ill it usually an overestimate of life expectancy."
Clwyd West MP Mr Jones, who was Wales Secretary under David Cameron, said: "Can you say what independent inquiries the Bill provides for that the judge should make?"
Mr Marris said: "Like many Bills, it doesn't fetter the discretion of a High Court judge in what inquiries they feel appropriate to make."
A shout of "that's reassuring" could be heard from the Tory benches.