We introduce a three-dimensional photoacoustic computed tomography (3D-PACT) system with unparalleled imaging depth, clarity, and speed, and demonstrate that the imaged structural and functional optical contrast provide a unique tool for preclinical research and an appealing prototype for clinical translation. 3D-PACT allows for multipurpose imaging of biological tissues ranging from the rodent brain to the human breast. In the rat brain, we visualized whole brain vasculatures, oxygenation dynamics, intrinsic functional connectivity, and electrical-stimulation-induced hemodynamics. In the human breast, an in vivo imaging depth of 4 cm has been achieved by scanning the breast within a single breath hold of 10 seconds. 3D-PACT holds a high reliability to reproducibly generate detailed images with a contrast similar to that provided by contrast enhanced magnetic resonance imaging, yet with higher spatiotemporal resolution and without using exogenous contrast agents.