There is little record of Williamson's activity until 6 July 1674, when he was denounced as a rebel for having held conventicles. In the following years, Williamson survived many narrow escapes from the law, including the incident memorialised in the song "Dainty Davie". In 1679, Williamson commanded a portion of the Covenanter army at the Battle of Bothwell Bridge. After Williamson's death, his son, John, related his father's escapades to Robert Wodrow. In George Lorimer's summary, Wodrow portrays Williamson as "a lonely hunted wanderer, glad of the shelter of a feal dyke behind which to lie down and rest himself amid the snow".