In 1941 Nicholls received his call-up notice and he joined the 29th Battalion but, in 1942, at the request of the Fitzroy police, he was released from his unit to work as a social worker in the Fitzroy Aboriginal community. He cared for those trapped in alcohol abuse, gambling, and other social problems, and those who were in trouble with the police. Indigenous people gathered to him and eventually the group was so large that he became the pastor of the first Aboriginal Church of Christ in Australia. In recognition of the ministry he was already expressing, he was ordained as a minister.