67 year old Noel Conway was diagnosed in 2014 and isn't expected to live beyond the next 12 months.
He wanted people with six months left to be allowed to choose how to end their own lives if they meet certain criteria.
On Thursday, two judges ruled against Conway at the High Court.
He plans to appeal the decision.
Speaking on News Hour, Christian campaigner James Mildred said he welcomed the ruling.
"We're pleased with the decision today, I recognise that for someone in Mr Conway's position there are very difficult issues that he is contending with and I recognise that there is severe and genuine pain and grief but I don't think that the answer is to introduce assisted suicide to the United Kingdom."
Mildred added that the introduction of assisted suicide into law may mean vulnerable people would be at risk.
"No matter how strict the criteria is, there will always be a danger that the criteria eventually gets expanded to include more and more people so you legitimise assisted suicide in more and more cases."
Listen to Marcus Jones speaking to James Mildred here: