Abstract Modular construction is experiencing an expansion in recent years as the need to integrate sustainability into the lifecycle of buildings becomes a key factor for engineering projects. The (i) reduced construction waste and recyclability of structural components over traditional building systems, (ii) rapid assembly with demountable capability and (iii) facilitated maintenance access contribute to make steel modular structures an optimized construction technique. Connections are major factors to determine the load‐transfer mechanism and overall structural performance of modular buildings. However, code limitations on design models for connections and methods to predict their influence on the global response of structural systems are aspects that must be addressed. This paper addresses the mechanical behaviour of a new preloaded inter‐modular connection developed within the R2U Technologies project. The connection comprises a long bolt ensuring the vertical continuity along stacked corner columns fixed at both ends and a joining block providing side‐to‐side continuity between modules. The load capacity of the connections was investigated based on axial and shear experimental tests validated through finite element (FE) models. Subsequently, from the identification of load transfer paths, component‐based models were developed to estimate the compression, tensile and shear resistance and stiffness of the connection. The resulting axial and lateral behaviours were implemented on 3D building structural models with the purpose of quantifying the influence and impact of the proposed inter‐modular connection on low and mid‐rise modular buildings in terms of load transfer and displacements. Overall, the long bolt connection proved to ensure the structural integrity and reliability of buildings under static loading conditions.