Multi-establishment firms (MEFs) rely on digitized processes enabled by advanced IT infrastructure, however, environmental dynamism is a major influence on their operations. Environmental dynamism threatens the efficacy of current operations, requiring firms to evolve their processes. Firms’ IT infrastructure may catalyze or hinder their endeavors and performance as they respond to the environmental dynamics. Little previous research examines which IT infrastructure types are high-performing and whether their effects vary across environments. We unravel the impacts of IT infrastructure, examining micro-level implementation–the constitution of technical and human assets–across the establishments of a multi-establishment firm (MEF). Specifically, we use the notion of a dominant IT infrastructure to unravel the heterogeneity of IT infrastructure across establishments. We unravel dominant IT infrastructure–technology, human, or both–and asses their impacts across environmental conditions. To test our hypotheses, we used a panel dataset comprising 355 unique firms, from 2007 to 2009. Findings reveal that the impact of establishment-level IT infrastructure types on MEF performance is contingent on the environment dynamism. A technology dominant IT infrastructure leads to greater MEF performance in less dynamic environments, while a human dominant IT infrastructure leads to greater MEF performance in more dynamic environments. The MEF performance is enhanced through a combination of technology and human in more dynamic environments. We discuss theoretical insights and managerial implications of our findings.