This paper describes experimental and numerical investigations focused on the shock-wave modification induced by a plasma actuator in the rarefied flow regime. The experimental investigation was carried out in the supersonic wind tunnel MARHy located at the ICARE laboratory, and the numerical investigation using a 2D fully compressible Navier–Stokes simulation was carried out at the IUSTI laboratory. The study concerns a cylinder in a Mach 2 air flow equipped with a small electrode that creates a local plasma. Electrical and optical diagnostics were used to experimentally analyse the plasma effects on the flow field. Measurements show that the shock stand-off distance increases with the discharge power. Numerical simulations show that the modification of the shock position is not induced by thermal effects. A theoretical approach is then developed in order to take into account the specific properties of plasma such as thermal non-equilibrium and ionization. It is found that the stand-off distance is directly coupled with the ionization degree of the plasma.