He was born in Skopje (now North Macedonia), to Ladino-speaking Sephardic Jewish parents, Max and Sarah, and spent his early years in Salonika, Greece, Izmir, Turkey and Beirut, Lebanon, before immigrating at the age of 16 with his family to New York.
[2] He received from the University of California, Berkeley in 1951 his Ph.D. under the supervision of Anthony Morse with thesis On the existence of functions having given partial derivatives on Whitney's curve.
From 1960 until he retired in 1989, Maurice Sion was a professor of mathematics at the University of British Columbia.
[1] In 1957 he was the coauthor with Philip Wolfe of a paper with an example of a zero-sum game without a minimax value.
[1] He greatly enjoyed travelling, taking several sabbatical years abroad.