Maintenance management remains a persistent challenge in Nigerian manufacturing, where reactive approaches dominate despite their well-documented inadequacies for achieving operational sustainability. This study examined the relationship between maintenance management dimensions (preventive, corrective, and predictive maintenance) and project sustainability indicators (cost control, minimal downtime, and asset lifespan) in manufacturing companies in Rivers State, Nigeria. A quantitative, cross-sectional survey design was employed, with data collected from 198 manufacturing companies using a structured questionnaire. Descriptive statistics, Pearson correlation, and multiple regression analysis were used to test the hypotheses. The findings revealed that preventive maintenance significantly positively affects cost control (β = 0.31), minimal downtime (β = 0.29), and asset lifespan (β = 0.27). Predictive maintenance demonstrated the strongest effects across all sustainability indicators (β = 0.47, 0.44, and 0.41, respectively). Corrective maintenance showed no significant relationship with any sustainability outcome. The study concludes that proactive maintenance strategies, particularly predictive maintenance, are essential for achieving project sustainability, while corrective maintenance delivers no measurable sustainability benefits. Theoretical contributions include empirical validation of the conceptual framework within the Rivers State manufacturing context. Practical implications advise manufacturing firms to prioritise investing in predictive maintenance technologies. Policy recommendations encourage regulatory incentives for proactive maintenance adoption. Limitations include the cross-sectional design and single-region focus.