Rev Dr John Dunmore Lang (1799-1878) was the founder of the Presbyterian Scots Church, Sydney and the first Presbyterian minister on mainland Australia arriving in May 1823. For the next 55 years he was one of the most prominent figures in colonial history. Lang wrote more than any other contemporary figure in Australian history. Lang’s extensive community involvement on behalf of his Church, his parliamentary career, efforts in immigration, newspaper publications and his desire to see a free and democratic society develop all carried Christian and nation building purpose. The controversial Scotsman could not be ignored. The mixture of responses to Lang’s life can be condensed to people either loved him or hated him. My thesis will seek both to explain and resolve this binary. Firstly, it places JD Lang back in a nineteenth-century Australian historical context. Secondly, it establishes Lang’s theological understanding and its application to the public life of colonial society. This is important because twentieth-century history writers have largely been critical of Lang. This is due in large measure to their failure to ask and answer the question ‘why’ regarding his service to his Church and society and their failure to allow for theological explanations. In view of this deficiency, the retrieval of Lang’s public theology will be my focus.