In mono- and multifilamentary MgB₂ wires with small filament diameters a homogeneous and fine-grained MgB₂ phase is required for high transport currents and reactions with the sheath have to be avoided. Taking this into account we developed very thin steel reinforced MgB₂ wires for application as current leads in a research satellite. In situ phase formation in the wire from Mg+B powders was chosen as the most favourable method to achieve good grain connectivity and thus high transport currents. We tested the current lead wires with transport current measurements and investigated the mechanical performance with applied tensile and bending strains. With an improved processing route applying a low-temperature anneal the superconducting properties of standard undoped in situ MgB₂ wires could be further improved and critical current densities of 38 kA cm⁻² at 6 T and 10 kA cm⁻² at 8 T, 4.2 K could be achieved.