Noel Conway, who's 67 and has motor neurone disease (MND), says he fears becoming "entombed" in his body as his muscles gradually weaken.
Mr Conway, from Shropshire, wants a doctor to be able to prescribe a lethal dose when his health deteriorates.
The case will be the first High Court challenge to the existing law since MPs rejected an attempt to introduce assisted dying in 2015.
It will also be the first such case since right-to-die campaigners lost their appeal before the Supreme Court in 2014.
The campaign group Dignity in Dying is supporting the legal bid.
Its chief executive, Sarah Wootton, told me:  "Noel's experience sadly echoes that of hundreds of other terminally ill people in this country - choice and control at the end of life is something that everyone should be able to have."
But Baroness Campbell, a disability rights campaigner, said the current law - the 1961 Suicide Act - was already compassionate and changing it would be "highly dangerous".
"Disabled people want to be valued by society and would see any legal change as a real threat."
Noel Conway, a retired college lecturer, was diagnosed with amyotrophic lateral sclerosis, a form of MND, in November 2014.
It is an incurable neurological condition that causes weakness and wasting in the limbs.
He is dependent on a ventilator overnight, requires a wheelchair and needs help to dress, eat and with personal care.
Speaking exclusively to the BBC, Mr Conway said he had been given a life expectancy of less than 12 months although his death might come sooner or later.
He told me: "I fear I will reach a stage where I am entombed in my own body as my ability to move gradually reduces - that would be unimaginable."
Mr Conway, who lives with his wife Carol and son Alex, used to be very physically active and enjoyed climbing, skiing, walking and cycling.
He told me he was not in any pain at present, but feared what would happen in his final weeks and that he might die by suffocation or choking.
"I have a right to determine how and when I die and I want to do so when I have a degree of dignity remaining to me," he said.
Carol Conway told me: "Noel's diagnosis was devastating. I do support him and think he should have the right to say enough is enough rather than fighting for breath and not being able to move.
"I can't help him end his life - we need the help of medical professionals to ease his passing."
Mr Conway has signed up with Swiss suicide group Dignitas but is concerned that when he is ready to die he might be too ill to travel.
He said: "I want to live and die in my own country. The current law here condemns people like me to unimaginable suffering - I'm heading on a slow, slippery slope to hell."
Noel Conway is seeking a judicial review of the 1961 Suicide Act, which makes it a criminal offence punishable by up to 14 years in prison for anyone to assist in a suicide.
His lawyers will seek a declaration that this is not compatible with the Human Rights Act 1998, which confirms that individuals should have respect for a private and family life.
This is the latest in a series of challenges to the law on assisted dying.
In 2014 the Supreme Court rejected an appeal concerning three disabled men who wanted doctors to be allowed to assist patients to die.
They had used similar legal arguments.  Five out of nine justices concluded that they did have the power to declare current law breached the right to a private life.
They did not make a "declaration of incompatibility" but two said they would have done so.
The Supreme Court made it clear that it was up to Parliament to deal with any decision on amending the law.
In September 2015 MPs rejected plans for a right to die in England and Wales, in their first vote on the issue in almost 20 years.
Noel Conway is the first terminally ill patient who is going to the High Court to argue for a right to an assisted death based on the failed vote in Parliament.
This case, which is expected to be heard at the High Court within a few months, will reopen a debate which has impassioned voices on both sides.
Those opposed to a change in the law argue that this issue has now been resolved for good by Parliament.
Baroness Campbell, who has spinal muscular atrophy, founded the organisation Not Dead Yet.
She uses a powered wheelchair, is fed through a tube and can now move only two of her fingers.
She told me: "If the law was changed it would feed into society's fear that being very disabled like me is a state worse than death.
"We already have to fight to live; a right to die would be a huge and frightening burden."
But Sarah Wootton from Dignity in Dying said the government had "ignored the pleas of terminally ill people" and said "Britain was being left behind".
Canada, California and Colorado all introduced assisted dying in 2016 and later this year the government in Victoria, Australia, plans to introduce legislation to allow doctors to help the terminally ill to die.
Meanwhile, in Shropshire, Noel Conway says he may not be well enough to travel to London for his High Court case and he realises it may not be resolved until after his death.
But he said: "Other countries have shown that assisted dying can work - it's been happening in Oregon for 20 years.  I want to ensure that terminally ill people like me don't have to suffer, and have a choice about their death."
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A terminally ill man has begun a legal fight for the right to die.