An Irish woman who is terminally ill with multiple sclerosis made an impassioned plea in her battle to seek the lawful right to die at the start of a landmark case in Ireland's High Court on Tuesday.

"I've come to the court, whilst I still can use my speech, my voice, to ask you to assist me in having a peaceful, dignified death, to die peacefully, I need assistance," Marie Fleming, 58, said, giving evidence from a wheelchair to three senior judges.

Fleming, whose partner wiped away tears as she spoke, was unable to sit in the dock and the judges came down from their usual elevated positions to sit on the normal benches and hear her evidence.