Sustainable travel behaviour is widely promoted, yet long-term sustainability depends on whether such behaviour becomes habitual. This systematic review examines how sustainable travel practices evolve into stable habits over time. Drawing on 36 empirical studies reviewed using the PRISMA framework, the paper synthesizes evidence across three interacting dimensions: travel motivation, financial factors, and cognitive factors. The findings show that motivation triggers initial engagement, financial feasibility enables continuity, and cognitive alignment supports consistency across repeated decisions. Habit formation emerges through the convergence of these conditions rather than through isolated interventions. The review clarifies how sustainable travel habits develop and highlights implications for research, policy, and practice.