Henkemans was born on December 23, 1913, in The Hague and died on December 29, 1995.
From 1926 to 1931 he was a pupil of Bernard van den Sigtenhorst Meyer, both for piano and composition, and from 1933 to 1938 he studied with Willem Pijper. Additionally, Henkemans studied medicine from 1931. In 1981, aged 67, he took his doctoral degree at the Amsterdam University with a thesis on Sublimation problems with artists, and their therapy (publ. Van Loghum Slaterus, 1981).
His debut as a pianist took place in 1945 in the Amsterdam Concertgebouw. After this first concert he remained active as a pianist for 23 years, performing 59 times as a soloist in the Concertgebouw, giving concerts in The Netherlands and abroad, and with no less than 20 gramophone recordings. As a pianist he has been famous for his Mozart and Debussy interpretations. In addition Henkemans taught composition and instrumentation at the Groningen Conservatory, and at the Amsterdam Muzieklyceum. He was also piano teacher. In 1969 he concluded his work as a concert pianist and since then devoted himself to psychiatry and to his work as a composer.
Henkemans published in periodicals such as the Netherlands Medical Review and Mens en Melodie. In 1961 the booklet Daar zit je dan ('And there you are sitting') was published (publ. Bert Bakker) with his "interim memoirs".
As a composer Henkemans was influenced by Debussy, Ravel, and Pijper. He characterized his style as "a way of composing tending to the utmost of pluritonal expression, however monotonal at bottom". He orchestrated the two Livres of Debussy's 24 Pr‚ludes. In 1932 he wrote his first Piano concerto (with string orchestra). In 1977 Henkemans concluded the opera Winter Cruise, based on one of the short stories by Somerset Maugham, for which he, himself wrote the libretto. This opera was given a dozen performances by the Netherlands Opera. Cello concerto (1988-89) was premiŠred in December 1990 by Dmitri Ferschtmann and the Radio Philharmonic Orchestra, Lucas Vis conducting.