[2] After his family moved to North Miami Beach, Florida, he attended a Conservative Hebrew school run by religious teachers, who convinced him to transfer to a yeshiva.
[2] At age 17 he progressed to the Telshe yeshiva in Cleveland, Ohio, where he received his rabbinic ordination[1] and became a close talmid (student) of Rabbi Mordechai Gifter.
[2][3] In 1983, Leff and his family decided to make aliyah to Israel, where he became the Rav and mora d'asra (rabbinic communal leader) of Moshav Matityahu, a small settlement now adjacent to Modi'in Illit (Kiryat Sefer).
[2] Leff has been a featured speaker at the conventions of the Orthodox Union, Agudath Israel of America, Torah Umesorah,[10] and the Association for Jewish Outreach Programs.
[12] In November 2018, a Sky News video of Leff engrossed in a sefer at a Scotland–Israel UEFA Nations League soccer game, oblivious to the excitement in the stadium after Israel scored its first goal, went viral.
[13] Leff and his wife had been visiting their daughter and son-in-law, the latter a UK Rabbanut chaplain for all the universities in Glasgow, and accompanied the entire community to dinner and the game.