Haddon King joined the Australian Army Engineers in 1941, and after work in Western Australia served in the Solomon Islands. On his return King accepted the position of Chief Geologist for Zinc Corporation at Broken Hill. At this time there was little geological mapping being undertaken there. However he was able to build on the detailed work that had been done by the joint Central Geological Survey under J.K. Gustafson between 1936-39, specially in regard to the layered structure of the orebody.
King later became Director of Exploration of the CRA group and led his organization during the discovery and development of Weipa, Bougainville and Hamersley, before retiring in 1970. However he continued to consult for these companies almost to the time of his death.
Building on the ideas of Arnold Black and others, King came to the conclusion in the early 1950s that the Broken Hill ores were essentially of sedimentary origin, and he expanded this work, with some enthusiastic assistants, to cover other lead-zinc deposits, the syngenetic concept being now widely accepted around the world. Haddon King always took time to think through his ideas, so he did not begin to publish extensively until relatively late in his career. However papers such as the Geology of the Broken Hill District (jointly with Bren Thomson), and The Broken Hill Lode (with E.S. (Tim) O'Driscoll) published in The Geology of Australian Ore Deposits (1953) began a significant period for economic geology, both Australia and worldwide.
The growth of Haddon King's ideas are set out in his semi-biographical The Rocks Speak (1989), which is sub-titled "Some personal responses of a willing listener" and published a short time before his death. He is commemorated by the Haddon Forrester King Medal awarded by the Australian Academy of Science, while Monograph 14 of the Australasian Institute of Mining and Metallurgy on the geology of the mineral deposits of Australia and Papua New Guinea is dedicated to his memory.