Kurt Alfred Georg Mendelssohn was born in Berlin in 1906. He attended the Goethe-Schule and Berlin University where he stayed on to do postgraduate research on low temperatures under his cousin, F.E. (later Sir Francis) Simon, receiving a D.Phil. in 1930. He remained at Berlin as a research assistant for a further year but in 1931 he followed Simon to Breslau where he had been appointed to the chair of Physical Chemistry at the Technische Hochschule.

While still at Berlin Mendelssohn had met F.A. Lindemann (later Lord Cherwell) who suggested that he should come to Oxford to carry out low temperature research at the Clarendon Laboratory, the intention being that he would begin work there in October 1933. In the meantime it was arranged that Mendelssohn should pay a brief visit to the Clarendon to instal a helium liquifier which he did in January 1933, thus becoming the first person to liquify helium in Britain. When Hitler came to power he decided to make an early return to Oxford and started work at the Clarendon in May 1933.

In the autumn of the same year Simon also came to Oxford, as did N. Kurti and H. London, all of whom contributed with Mendelssohn to the establishment of the Clarendon as an important centre of low temperature research. However, with the advent of the Second World War the low temperature apparatus had to be dismantled and Mendelssohn turned to various collaborative projects in medical physics. After the war he resumed his work on low temperatures in collaboration with a succession of gifted research students, many of whom built up graduate schools of their own after leaving the Clarendon, thus making their mark in low temperature centres all over the world. He was elected Fellow of the Royal Society in 1951. He was awarded the Royal Society's Hughes Medal in 1967 and the Simon Memorial Prize in 1968.

In addition to his research work in the laboratory Mendelssohn was closely involved with other low temperature scientists at the international level. He was Chairman and founder member of the International Cryogenic Engineering Committee, President of Commission A2 of the International Institute of Refrigeration, and founder and general editor of the journal Cryogenics. He published two books on low temperature physics and was very active as editor and contributor to other monographs and journals. Through his contacts with foreign research students he also actively encouraged attempts to establish new centres for low temperature research, particularly in developing countries. He made great efforts to establish formal links between Wolfson College, Oxford, and academic institutions in Ghana, India and Portugal.

In 1960 Mendelssohn paid his first visit to China and this laid the foundations of an abiding interest in the country and its scientific and cultural development. Mendelssohn's other main 'extra-mural' interest was the sociological and engineering background of the Egyptian and Mexican pyramids, on which he also published a book and several articles in both popular and learned journals.

Mendelssohn retired in 1973. He was diagnosed as suffering from Parkinson's disease in 1976, from which he died in 1980.