Professor McMahon gained prominence in hydrology during the seventies when he jointly conducted workshops in Australia and overseas for practising water engineers. However, he is best known internationally through published research in stochastic hydrology. Of particular significance is his text-book for post­graduates and professional engineers which deals with storage-yield analyses for large reservoirs.
He was also recognized as a world authority by being invited to chair UNESCO's Low Flow Hydrology Panel. This resulted in another book published in both English and Russian for use by engineers mainly in developing countries.

In 1985, Professor McMahon presented a paper on "Flooding in Australia" to the Academy's National Disasters Symposium.