A discontinuous Galerkin method is proposed for computing the current density in superconductors characterized by a constitutive power law between the current density and the electric field. The method is formulated to solve the nonlinear diffusion problem satisfied by the electric field, both in the scalar and 2-D vectorial case. Application examples are given for a superconducting cylinder subjected to an external magnetic field. Results are compared to those given by the mixed finite-element/finite-volume method and those obtained using a standard finite-element software. Efficiency and robustness of the approach are illustrated on an example where the exponent in the power law is spatially dependent.