UNLABELLED: Reading is one of the most complex skills that we utilize daily, and it involves the early development and interaction of various lower-level subskills, including phonological processing and oral language. These subskills recruit brain structures, which begin to develop long before the skill manifests and exhibit rapid development during infancy. However, how longitudinal trajectories of early brain development in these structures support long-term acquisition of literacy subskills and subsequent reading is unclear. Children underwent structural and diffusion MRI scanning at multiple timepoints between infancy and second grade and were tested for literacy subskills in preschool and decoding and word reading in early elementary school. We developed and implemented a reproducible pipeline to generate longitudinal trajectories of early brain development to examine associations between these trajectories and literacy (sub)skills. Furthermore, we examined whether familial risk of reading difficulty and children's home literacy environments, two common literacy-related covariates, influenced those trajectories. Results showed that individual differences in curve features (e.g., intercepts and slopes) for longitudinal trajectories of volumetric, surface-based, and white matter organization measures were linked directly to phonological processing and indirectly to first-grade decoding and word reading skills via phonological processing. Altogether, these findings suggest that the brain bases of phonological processing, previously identified as the strongest behavioral predictor of reading and decoding skills, may already begin to develop by birth but undergo further refinement between infancy and preschool. The present study underscores the importance of considering academic skill acquisition from the very beginning of life. SIGNIFICANCE STATEMENT: Reading is crucial for academic, vocational, and health outcomes, but acquiring proficient reading skills is a protracted developmental process involving lower-level subskills and brain structures that undergo rapid development starting in infancy. We examined how longitudinal trajectories of early brain development support long-term acquisition of reading using a reproducible pipeline we developed specifically for infant-to-school-age longitudinal MRI data. Findings suggest that the brain bases of reading-related skills begin to develop by birth but continue building between infancy and preschool. This study emphasizes the importance of considering academic skill acquisition as a dynamic process preceding the emergence of the skill, and it offers a roadmap for future studies to examine relationships between early brain development and academic skill acquisition.