He was also one of the founders of kibbutz Ein Gev and a longtime assistant director of the Yad Vashem memorial center.

In the early 1930s, Dafni was studying in Vienna, where his father was a diplomat: he was a keen athlete, a member of the student union and an activist in the Zionist youth movement.

After the war he returned to his kibbutz, but in 1946, as a member of the Haganah, Dafni went to the United States to raise funds and purchase weapons for the defence of the Yishuv; one of his contributors was Bugsy Siegel.

For 13 years, from 1983 to 1996, Dafni served as assistant director, in Jerusalem, of Yad Vashem: Israel's official memorial to the victims of the Holocaust.

Dafni was married to Rina (née Grossman) with whom he had two children, a son, Yoram, and a daughter, Avital.