Hennessy & Hennessy was an architectural firm established in 1912 in Sydney, Australia that was responsible for a series of large scale office buildings in the 1930s in all capital cities in Australia, as well as New Zealand and South Africa, designed by John (Jack) Hennessy (1887–1955), described as Australia's first international architect.

John Francis (Jack) Hennessy (1887–1955) was an Australian architect, with the same name as his architect father, John Francis Hennessy, with whom he was in partnership as Hennessy & Hennessy from 1912 to 1924. As principal of the firm after his father retired from 1924 to 1955, he was responsible for many major Art Deco office buildings in capital cities in Australia and New Zealand in the 1930s, as well as many projects for the Catholic Church in Queensland, and the Great Court of the University of Queensland.