Optical and infrared monitoring of the afterglow site of gamma-ray burst GRB 031203 has revealed a brightening source embedded in the host galaxy, which we attribute to the presence of a supernova (SN) related to the GRB (``SN 2003lw’'). We present details of the discovery and evolution of SN 2003lw from 0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I and J bands. GRB 031203 was an intrinsically faint GRB, and the optical light curve is dominated by the SN after the first few days. A template Type Ic light curve, constructed from SN 1998bw photometry, is consistent with the peak brightness of SN 2003lw, although the light curves are not identical. Differential astrometry reveals that the SN, and hence the GRB, occurred less than 300 h$^-1$$_71$ pc (3 σ) from the apparent galaxy center.