Johnston started a career in social work and social management in Hong Kong where he was born, after graduating in Sociology from Brock University, Canada. He acquired extensive experiences in applying case, group and community approaches to youth work, family life education, school social work, civic education and health education. He has taught at primary, secondary and tertiary levels and acted as administrators in schools and healthcare organizations. He is one of the founders and now Member of Board of Directors of the Social Workers Across Borders, a NGO registered in Hong Kong devoted primarily to disaster social work intervention. Since 2006, he resides and teaches social work and social administration in Zhuhai, China, with the Beijing Normal University Hong Kong Baptist University United International College.

Disaster Social Work, Social Work in Health Care, Positive Psychology and Post-traumatic Growth, Industrial Health and Occupational Social Work, Working with Youth, Student Development in Higher Education, Emotional Intelligence, Adversity and Resilience, Social Innovations and Enterprises, International Social Work.