Sionagh received her BVMS degree from the University of Glasgow in 1990. After 4 years in mixed practice, she undertook a PhD in the Department of Veterinary Pathology at the University of Edinburgh, focusing on epidemiological and pathological aspects of porcine proliferative enteropathy. In 1997 she began a residency position at the University of Pennsylvania in Philadelphia and became a diplomate of the American College of Veterinary Pathologists in 2000. She remained in Philadelphia as a lecturer for an additional year. After two years with Idexx Laboratories in the UK, she joined the faculty at the University of Tennessee College of Veterinary Medicine, as Assistant Professor of Veterinary Pathology. In 2005, she joined the Royal (Dick) School of Veterinary Studies where she is currently Senior Lecturer of Veterinary Pathology and Head of Anatomic Pathology.