The Scottish actor's dad, 77-year-old Reverend Sandy MCDonald, is suffering from lung condition pulmonary fibrosis, and now lives in a hospice, where he is cared for.
Following this revelation, MCDonald has called on senior religious figures in the U.K. to support the Assisted Suicide Bill, which aims to allow those who are terminally ill decide their own fate.
He tells Scotland's The Herald newspaper, "I have pulmonary fibrosis. It just gets worse. There is no cure. I have to address it and decide what to do. I have an advance directive which says 'do not resuscitate.' I do not want to be fed by something in my stomach.
"What I do want is the right to a peaceful end to my life. I think we have the wrong slant, the wrong emphasis. The phrase - assisted suicide - has criminal overtones in the minds of many people. We need to take seriously the provision of a peaceful end of life for all those who want it. Of course there would have to be safeguards, and that should be discussed."
Tennant dedicated his special recognition accolade at the National Television Awards to his father in January (15).