Kalckar received his early schooling in the Ostre Borgerdyd Skole. He completed his studies for a degree in medicine at the University of Copenhagen in 1933.
Kalckar began his scientific career in 1934 as a candidate for the Doctor of Philosophy degree in the Department of Physiology at the University of Copenhagen under the direction of Ejnar Lundsgaard.
Kalckar’s early experiments on oxidative phosphorylation also provided evidence for the production of phosphoenolpyruvate from fumaric or malic acids, observations that later provided an important clue to the mechanisms involved in the formation of glucose from noncarbohydrate sources in animal tissues. In 1939, having completed his work for the Doctor of Philosophy degree, Kalckar was appointed a Rockefeller research fellow for a year of postdoctoral study at the California Institute of Technology.
In 1940, Kalckar accepted an appointment as research fellow in Cori’s Department of Pharmacology at Washington University. He joined forces with Sidney Colowick. Their work led them to the discovery in muscle extracts of a remarkable enzyme, named myokinase by them, but now more precisely called adenylate kinase.
In 1943, Kalckar was appointed research associate at the Public Health Institute of the city of New York. Three years later, he returned to Copenhagen, where a new laboratory was set up for him with the support of Ejnar Lundsgaard and with financial backing from American as well as Danish sources.
In 1952, Kalckar began his studies on the metabolism of galactose in microbial and animal tissues. This became a principal pursuit after his move to the National Institutes of Health in 1952, first as a visiting scientist and later with a permanent appointment at the National Institute of Arthritis and Metabolic Diseases.
In 1958, he accepted a professorship in the Department of Biology of Johns Hopkins University. This year also marked the publication of his highly original proposal that the contamination of foodstuffs from the fallout following atmospheric tests of nuclear weapons could be measured by the analysis of the content of strontium-90 in the milkteeth of young children.
In 1961, Kalckar moved to the Harvard Medical School as professor of biological chemistry and head of the Biochemical Research Laboratory of Massachusetts General Hospital (MGH). There he continued his studies on the metabolism of galactose in animal tissues with special attention to the epimerase. Thirteen years later, he retired from the hospital but continued his research as visiting professor in the Huntington Laboratories at MGH until 1979. At that time he moved to the Department of Chemistry at Boston University as distinguished research professor. Kalckar continued his work on hexose transport and metabolism in normal and malignant cells in the laboratory at Boston University and that was the subject of many papers with his longtime collaborator, Donna Ullrey.
Kalckar was a member of National Academy of Sciences, the Royal Danish Academy and the American Academy of Arts and Sciences.
The sweep of his intellect was very broad, his spirit was open and generous and he had a wonderful sense of humor.
Herman Kalckar was married to Vibeke Meyer, with whom he divorced in 1950. He was married to Barbara Wright. They had 3 children, Sonja, Nina and Niels. In 1968, he married Agnete Fridericia Laursen.