As commissioner, he directed the evacuation of European settlers from the Solomon Islands prior to the Japanese occupation of the islands during World War II as well as leading the organisation of coastwatcher units throughout the islands. Marchant relocated from this headquarters at Tulagi to Malaita about two months before the Japanese occupied Tulagi in May, 1942. On Malaita he helped operate a coastwatcher radio relay station in support of the Allied Solomon Islands campaign until the end of his appointment in 1943.