We present the first deep, optical, wide-field imaging survey of the young open cluster Collinder 359, complemented by near-infrared follow-up observations. This study is part of a large programme aimed at examining the dependence of the mass function on environment and time. We have surveyed 1.6 square degree in the cluster in the I and z filters with the CFH12K camera on the Canada-France-Hawaii 3.6m telescope down to completeness and detection limits in both filters of 22fm0 and 24fm0, respectively. Based on their location in the optical (I-z,I) colour-magnitude diagram, we have extracted new cluster member candidates in Collinder 359 spanning 1.3-0.04 M&sun;, assuming an age of 100 Myr and a distance of 450 pc for the cluster. We have used the 2MASS database as well as our own near-infrared photometry to confirm the membership of the optically-selected cluster candidates. Additionally, we have obtained optical spectroscopy and employed chromospheric activity as a further criterion to assess the membership of candidates.