Mudstone is the most abundant sedimentary rock and its low permeability and high compressibility contribute to overpressure in marine systems around the world. Despite its fundamental importance as source, seal, and shale gas/oil reservoir in petroleum systems or as seal for anthropogenic-related storage, a systematic, process-based understanding of the controls on hydromechanical properties in mudstones remains elusive. We fabricate mudstones from natural, marine sediments acquired through the International Ocean Discovery Program using the resedimentation technique and compress them to simulate deposition and burial. Then we analyze their hydromechanical properties such as porosity, compressibility, permeability, and fabric, which are strongly influenced by particle size and mineralogy. For example, mudstone porosity and compressibility decrease with decreasing clay fraction while permeability increases due to the development of a dual-porosity system, where large pores between silt grains are preserved leading to high permeability pathways within the clay matrix containing small pores. Our results carry fundamental implications for a range of problems in mudstone related systems, with relevance for carbon sequestration, hydrocarbon trapping, basin modeling, overpressure distribution, submarine slope stability, and understanding of gas-shale behavior.