According to one account, the Visionary was a Time Lord who, upon looking into the Untempered Schism, was driven mad by what she saw. (PROSE: A Brief History of Time Lords) According to another account, she belonged to the Sisterhood of Karn and was added to the War Council by Rassilon when he decided to be more personally involved in the conduct of the Time War. (AUDIO: Homecoming)
She was present at a High Council meeting presided over by Lord President Rassilon during the war. She foretold that Gallifrey would burn, as she wrote Gallifreyan symbols onto a piece of paper with an ink pen.
She screamed "Gallifrey falling... Gallifrey falls!" as Rassilion's plan to bring Gallifrey back failed at the hands of the Tenth Doctor, sending the planet back into the last day of the Time War. (TV: The End of Time)
When Gallifrey managed to survive the Time War, (TV: The Day of the Doctor) Rassilon began to fear that the Visionary had instead foreseen the coming of the Hybrid. (PROSE: A Brief History of Time Lords)
By the end of the war, she was showing signs of insanity and constantly in a frantic state, spouting puzzling words and phrases which alluded to events due to happen in the future. When she was silent, the Visionary would scrawl pieces of paper with her prophecies in Gallifreyan text that was difficult to read. (TV: The End of Time)