McWilliams attended the Vancouver School of Art and began exhibiting in the late 1960s in Vancouver. He was a curator at the Burnaby Art Gallery (1972-75) and also taught at Douglas College, the Banff Centre for the Arts, and ECCAD. His work was included in Aurora Borealis, Montreal 1985, and in Vancouver Art and Artists and Kunstlerhaus Canada in 1983, among other exhibitions, and he has done a number of public art commissions. In a 1982 interview with Jo-Ann Birnie Danzker at the VAG, McWilliams said an art work's "presence is not in its specificity but in the state of mind it engenders, in its resonances.... expect the viewer to ask questions, questions about their cultures, their belief systems, themselves."