Modular construction can become sustainable by making all aspects of the design and construction process more effective during all phases. This paper aims to develop and use a sustainability assessment model for modular residential buildings in two case studies. This research uses the Integrated Value Model for Sustainable Assessment (MIVES), which is a multi-criteria decision-making model for sustainability assessment. This model considers all aspects of sustainability, environmental, economic and social, and helps stakeholders make decisions. Few previous studies have assessed all these aspects in full and MIVES make this assessment possible. For assessment purposes, two modular buildings have been chosen, namely “Ten Degrees Croydon” as the tallest high-rise modular residential building in the world and “Apex House” as the second tallest modular building in the world, both in London. These residential towers were assessed using MIVES, demonstrating a very satisfactory sustainability index in all the above aspects.