In this study, slag waste was incorporated as cement replacement in steel fiber reinforced concrete (SFRC), and the subsequent effect on durability in marine environment is investigated. Two replacement ratios (30% and 50%) of slag were used, and the corresponding properties pertaining to chloride ion penetration were determined by NT Build 492. Long term behavior under marine environment exposure was also evaluated by immersing the concrete specimens in seawater at the East Sea of South Korea. Also, probabilistic methods were employed to predict service life of the developed concretes based on chloride attack. The results clearly indicated that GGBS incorporation leads to improved durability attributes as indicated by reduced penetration depth and lower migration coefficient of chloride ions for all GGBS incorporated specimens. The long-term durability evaluation also corroborated the beneficial effects of GGBS on concrete durability. Further, the probabilistic service life assessment showed that GGBS addition led to significantly higher (more than seven times) service life, as set by the criterion of chloride ion penetration up to 50 mm. The usefulness of GGBS in improving durability of plain as well as steel fiber reinforced concrete points towards effective waste utilization in construction and building materials with improved durability and service life in marine environment.