On 8 April 1891, Monash married Hannah Victoria Moss (1871–1920), and their only child, Bertha, was born in 1893. Monash had previously engaged in an affair with Annie Gabriel, the wife of one of his colleagues, which ended as an active matter after his conscious choice of 'Vic' for marriage (though communication continued many years afterwards). He worked as a civil engineer, and played a major role in introducing reinforced concrete to Australian engineering practice. He initially worked for private contractors on bridge and railway construction, and as their advocate in contract arbitrations. Following a period with the Melbourne Harbor Trust, in 1894 he entered into partnership with J. T. N. Anderson as consultants and contractors. When the partnership was dissolved in 1905 he joined with the builder David Mitchell and industrial chemist John Gibson to form the Reinforced Concrete & Monier Pipe Construction Co, and in 1906 with them and businessmen from South Australia, to form the S. A. Reinforced Concrete Co. He took a leading part in his profession and became president of the Victorian Institute of Engineers and a member of the Institution of Civil Engineers, London.