Noel Conway has motor neurone disease and has been given around nine months to live. When he has less than six months left, he wants to be able to end his life.
He started his fight at the High Court to change the law on assisted dying on the morning of Monday 17th July.
Conway, who is supported by Dignity in Dying, has already been to the Court of Appeal to win the right for what he calls his "fight for choice at the end of life" to proceed.
He said: "I am more determined than ever to continue.
"I have the support of my loved ones and many thousands of others behind me; people who have donated over £90,000 towards my legal costs and sent heart-warming messages of encouragement to me and my family.
"I have lived my whole life on my own terms, in control of the choices and decisions I make.
"Why then, when I am facing my final months, should these rights be stripped away from me, leaving me at the mercy of a cruel illness?
"I know I am going to die anyway, but how and when should be up to me.
"To have the option of an assisted death available in this country would provide me and countless others with great reassurance and comfort.
"It would allow me to decide when I am ready to go, rather than be forced into a premature death by travelling to Dignitas at great emotional and financial cost, or to suffer a traumatic, drawn-out death at home."
Nikki and Merv Kenwards, of the Distant Voices campaign group, will demonstrate their opposition to Conway's legal bid with a giant puppet display outside the High Court, including an enormous judge holding a syringe.
We are with Nikki and Merv campaigning outside the Royal Courts of Justice against assisted dying pic.twitter.com/OVMBPShtxz
— Christian Concern (@CConcern) July 17, 2017
They want to convey a message that assisted suicide would "undermine the dignity of human life and put vulnerable lives at risk".
Nikki Kenward was left paralysed in 1990, at the age of 37, by Guillain-Barre Syndrome, and for several months was only able to wink her right eye. Now, she remains wheelchair-bound.
She said that if she had had the choice to die during her five months in hospital, she would have chosen death, and that the hospital staff treated her as "worthless".
However, she said that "her spirit fought to live" and now firmly opposes any liberalisation of the law.
She believes that if euthanasia becomes an option in our society, it will further degrade our attitude towards the dignity of life, leaving many vulnerable to being euthanised against their will – including children and those with mental health conditions.
CLC clients Nikki and Merv Kenward are demonstrating on Monday morning to bring to the public's attention to the dangers of assisted suicide pic.twitter.com/oMQ3oSKQaj
— Christian Concern (@CConcern) July 15, 2017
"We have seen from other countries where assisted suicide and euthanasia have been legalised, that this has loosened vital protections for the most vulnerable in society. In these countries, people are being euthanised even for mental health conditions such as depression.
"This must serve as a warning to our nation to firmly resist these ongoing attempts to liberalise the law."
This is the first High Court challenge to assisted suicide law, since the defeat of Rob Marris' bill to legalise it in 2015.
Conway will not attend the five-day hearing in London before Lord Justice Sales, Mrs Justice Whipple and Mr Justice Garnham. It is expected that a ruling will not be given until the autumn.