We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the KPNO 4-m telescope. We describe our data reduction and automated photometry techniques in some detail, as we will shortly perform a similar analysis of other Local Group galaxies. The present study covered 2.2 square degrees along the major axis of M31, and 0.8 square degrees on M33, chosen so as to include all of the regions currently active in forming massive stars. We calibrated our data using data obtained on the Lowell 1.1-m telescope, and this external method resulted in millimag differences in the photometry of overlapping fields, providing some assurance that our photometry is reliable. The 1 Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under NASA contract NAS 5-26555. These observations are associated with program GO-9794.