Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter it is required to study materials under multi-extreme conditions, in particular down to very low temperatures, in very high magnetic fields, as well as under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross-section of (0.5~mm)$^2$. We describe the design and performance test of the dilatometer which resolves length changes with high resolution of $0.02 mathrm{AA}$ at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system.