In this paper, the digital design and manufacturing of a post-tensioned concrete girder is presented. We bring together two emerging technologies that show great potential for realizing highly-efficient concrete structures: topology optimization for simulation-driven design and 3D concrete printing (3DCP) for manufacturing of optimized shapes. While this is not the first-ever 3D-printed concrete structure, it is the first demonstration of how topological design in combination with 3D concrete extrusion printing allows for creating efficient structures with reduced use of materials. As the implementation of a specific optimization procedure for post-tensioned concrete structures is so far available in 2D only, some design post-processing was necessary, and a 3D finite element analysis was performed. After realization of the 3DCP element (i.e. printing and assembly), the girder's structural performance was experimentally verified using digital image correlation. The deflection of the girder was compared with the numerical results. The manuscript includes thorough discussions on the manufacturing challenges – including printing setup, assembly and integration of reinforcement. Display omitted •Digital design-to-manufacture process of a post-tensioned concrete girder•Unique and concurrent topology and shape optimization procedure•3D concrete printing, post-tensioning and grouting to realize the optimized design•Experimental verification of the girder's load-carrying capacity•Demonstration of 3D printing for optimized structures, enabling significant material reduction