"He died basically of lung cancer, but he actually died of a morphine overdose. Why would I want to see him suffer in pain in the last days of his life?
"In my mind ... if I get to the point in my life where I am terminally ill and I have no quality of life or dignity in my life, I think I would want to die sooner rather than later."
He later told the Herald his father-in-law, whom he declined to name, was hooked up to a morphine pump.
"People have told me that usually at the ultimate stage, they'll keep lifting the morphine level to keep the pain away, and you may die from the morphine and not from the cancer," Mr Goff said.
"Nobody thinks that's wrong. Nobody thinks you should have to die in pain and live a couple of days longer, rather than have a level of morphine that may be responsible for loss of life.
"Any doctor would be quite comfortable with that happening. It's a no-brainer, really."
In conscience votes Mr Goff has twice voted in favour of bills allowing euthanasia - once in 1995 and again for the Death with Dignity Bill in 2003. Both bills were eventually voted down. He said he would support another bill on euthanasia at least as far as a select committee.