Born in Ridderkerk, Kaashoek has studied mathematics at the Leiden University, where he received his Phd in 1964 under supervision of Adriaan Zaanen.
Kaashoek had started his academic career as assistant at the Leiden University from 1959 to 1962, and Junior Staff Member from 1962 to 1965.
He was elected honorary member (erelid) of the Royal Dutch Mathematical Society (Koninklijk Wiskundig Genootschap) on 22 March 2016.
M. A. Kaashoek is one of the early supporters of the International Workshop on Operator Theory and its Applications (IWOTA), which was started in 1981.
[3] From the beginning, M. A. Kaashoek and J. W. Helton served as vice presidents of the IWOTA Steering Committee.