We present g' and z' aperture photometry for 96 Galactic globular clusters, making this the largest homogeneous catalogue of photometry for these objects in the Sloan Digital Sky Survey (SDSS) filter system. For a subset of 56 clusters, we also provide photometry in r' and i'. We carry out comparisons with previous photometry as well as with the SDSS data set. The data will be useful for a series of applications in Galactic and extragalactic astrophysics. Future papers will analyse the colour-metallicity relation, colour-magnitude diagrams and structural parameters. The compilation of results based on this data set will be collected in the Galactic Globular Cluster Catalog (G2C2).