Harold Helgeson was born on November 13, 1931, in Minneapolis, Minnesota and grew up in St. Paul, Minnesota. After completing his BS degree in Geology at Michigan State University, he worked for a year in 1953/54 as an exploration geologist for Technical Mine Consultants in Athabasca, Saskatchewan /Northwest Territories, and Blind River, Ontario, after which he served for two years during the Korean War as a photo-radar intellegence officer in the 497th Recon Tech Squadron of the U.S. Air Force in Wiesbaden, Germany.

After his military service he spent 4 years as a mining and exploration geologist for Anglo-American Corporation in South Africa, first in diamond exploration for the DeBeers subsidiary of the company in Southwest Africa, and then as an underground mining geologist on the President Steyn Gold Mine in Welkom, South Africa, and the Nkana Copper Mine in Kitwe, Zambia. In 1959 he returned to the United States where he briefly attended Stanford University, followed by a summer season of gold exploration in British Columbia and Alaska. He then went on to obtain his Ph.D. degree from Harvard University, where he studied with Bob Garrels.

After receiving his Ph.D. in 1962, he worked as a Research Chemist for Shell Development Company in Houston, Texas, and the geothermal field near the Salton Sea in California. In 1965 he joined Bob Garrels at Northwestern University, where he began his teaching career. In 1970 he joined the faculty of the University of California, where he has continued to teach and carry out theoretical research and consulting in high temperature/pressure solution chemistry, thermodynamics and kinetics of hydrothermal/geothermal systems, inorganic and organic geochemistry, biogeochemistry, and the chemical interaction of minerals, microbes, and aqueous inorganic, organic, and biochemical species in geochemical processes.