Re'em HaCohen was born in Jerusalem on 1 March 1957 to Yedaya, a principal at Yeshivat Har Etzion and son of Zionist thinker Shmuel HaCohen Weingarten (he), and Dina, head of Midreshet Emuna and daughter of Zionist pioneer Natan Gardi (he).

In his youth, Hacohen would frequently visit the house of Rabbi Shlomo Zalman Auerbach.

In 1994, he was invited by rabbis Binyamin Kalmanzon and Ami Ulami to be a Rosh Yeshiva at Yeshivat Otniel.

He serves on the judging panel of "Kane Lecha Chaver", a Torah competition run by Mifal HaPayis.

His brother-in-law is Rabbi Aharon Harel, head of Lev Chadash Yeshiva High School in Shilo.

He is a student of Kabbalah, especially the teachings of the Ramchal, Chabad (in particular the Baal HaTanya) and Menahem Azariah da Fano.