The fashion industry has expanded at the expense of the environment. Consumption and environmental pollution both serve as a wake-up call to the global endeavour to adopt more socially and environmentally responsible behaviours. It implies, in particular, a paradigm shift in consumer behaviour away from conventional to green products. Understanding the factors that influence consumer purchasing decisions is critical in developing the demand for and commitment to sustainable apparel consumption. In support of the United Nation’s efforts to promote sustainable consumption in Malaysia, a study was conducted to determine the motivating factors that influence consumers’ purchase intentions for sustainable apparel. The moderating effect of fashion consciousness on the outcome was also examined. An extended model of the Motivation-Opportunity-Ability (MOA) Theory and Self-Determination Theory (SDT) was developed and tested using 324 responses collected from the Malaysian millennial generation in six major urban locations. The results of the structural equation modelling analysis indicated that the elements of motivation, opportunity, and ability were all positively linked with the sustainable apparel purchase intention. Fashion consciousness had a moderating effect on the relationships between the three drivers (motivation, opportunity, and ability) and purchase intention. The research findings provide valuable insights for businesses to formulate a sustainable and unified business model that incorporates environmental, social, and consumer considerations into core business practices. These insights would also help designers to advance the development of sustainable products as an area of innovation and support policymakers in achieving the UN’s 17 Sustainable Development Goals (SDGs).