Mossinson, son of Asher Mossinson and his wife Dvora, was born in Ottoman Palestine in 1917, in the moshav Ein Ganim, located near Petah Tikva; he grew up in Tel Aviv. Later on Mossinson studied in Beit Alfa and in the youth village of Ben Shemen. Afterward he moved to the Kibbutz Na'an, where he lived from 1938 to 1950. In 1943 Mossinson joined the Palmach. During that period Mossinson was arrested by the British and imprisoned in Latrun. In 1944 Mossinson published his first story in the newspaper Al HaMishmar. During the 1948 Arab–Israeli War Mossinson served as a cultural officer in the Givati unit.
In 1953, following the publication of the novel A Man's Way (Hebrew: דֶּרֶךְ גֶּבֶר), Mossinson had to leave the kibbutz; he moved to Moshav Beit Shearim. From 1952 Mossinson served for a year and a half as a press spokesman for the Israeli police and afterward as the spokesman for the Habima Theatre.
In 1957 Mossinson founded the Sadan Theatre in the Mughrabi Hall. The theatre went bankrupt eventually and closed. In 1959 Mossinson moved to the United States where he pursued various businesses for a living. During this period he helped adapt the play Casablan for the screen, with a film version (filmed in Greece) released in 1964. In 1965 Mossinson returned to live in Israel, where he began his literary career
