He was the son of Rabbi Zvi Hirsch Bengis, the Rabbi of the Russian Empire (now Lithuanian) town of Šnipiškės (now a neighborhood of Vilna) and his wife Shayna, the granddaughter of Rabbi Aaron Brody, dayan of Vilna. After having learned in Volozhin for several years, he married the daughter of Rabbi Chaim Tzvi Broide, Rav of the towns Nemakščiai (Nemoksht in Yiddish), Švėkšna (Shvkshna in Yiddish) and Žagarė (Zhager in Yiddish).
He wrote a seven-volume commentary on the Talmud, called "Leflagos Reuven". Rabbi Zelig Reuven was soon known as "the Shnipishoker illui" (prodigy). When he was 17 years old, he went to learn in the Volozhin yeshiva under the Netziv, who called him "the living Shas".
While learning at Valozhyn, his reputation quickly grew and he was known as an extremely sharp student and a diligent learner.
In 1892 he was appointed Rabbi of Boćki (Bodki), Poland, succeeding Rabbi Malkiel Tzvi Tenenbaum who took the position of Rabbi of Lomza. After having spent 19 years as Rav of Boćki (Bodki), in 1911 he became the Rav of Kalvarija, Lithuania.
During his time as Rav of Kalvarija, World War I broke out. During the war, the Russian government forced Jews to move further eastward.
Rabbi Bengis settled in Smolensk, a Russian town where many non-religious Jews lived.
In this, he received strong encouragement from the Chofetz Chaim. After the war, Bengis returned to Kalvarija. He received halachic questions from all over the world.
Some of his halachic rulings were published in the periodical HaTevunah, but they were never published in bookform.
In 1932, after the death of Rabbi Yosef Chaim Sonnenfeld, Bengis was asked to become rosh av beit din (Ravad) - 2nd Chief Rabbi - of the Edah HaChareidis in Jerusalem. However, the leadership of the Edah repeated their offer in 1937.
Since Rav Kook had died, Rabbi Bengis accepted the offer, and moved from Lithuania to Palestine - shortly before World World War II broke out. In 1947, he and Rabbi Yosef Tzvi Dushinsky, the Chief Rabbi - Gaavad - of the Edah, appeared before a United Nations commission which was to decide the future of the British Mandate of Palestine.
They spoke against the establishment of a Jewish state there, requesting the United Nations to recognize Jerusalem as a holy city which should not be part of any state, but should be ruled by the United Nations itself as an international city.
He also requested the commission to allow the immigration of homeless Jews who had survived the war in Europe. When Rabbi Dushinsky died in 1948, Bengis succeeded him as govad of the Edah. Simultaneously, he also fulfilled the position of Rosh Yeshiva at Yeshivas Ohel Moshe, also in Jerusalem.
Bengis died on the 7th of Sivan, 5713 (21 May 1953).
He was almost 90 years old, and had fulfilled rabbinical roles in Lithuania and Jerusalem for over 60 years. He was interred on Har HaMenuchot.
