Born in Motal, near Pinsk, Russian Empire (now Belarus), he studied at the Orthodox yeshivot of Malch, Slobodka, and Novardok, where, at age 18, he received his smicha, the Jewish equivalent of ordination.

Lieberman's decision was motivated by a desire to "train American Jews to make a commitment to study and observe the mitzvot.

54–63, Prof. Haim Dimitrovski relates that when he was newly hired at JTSA, he asked Rabbi Menachem Mendel Schneerson of Lubavitch whether he should remain in the Seminary, and the response was "as long as Lieberman is there."

His preoccupation with the Jerusalem Talmud impressed him with the necessity of clarifying the text of the tannaitic sources (rabbis of the first two centuries of the common era), especially that of the Tosefta, on which no commentaries had been composed by the earlier authorities (Rishonim), and to whose elucidation few scholars had devoted themselves in later generations.

The latter combined philological research and historical observations with a discussion of the entire talmudic and rabbinic literature in which the relevant Tosefta text is either commented upon or quoted.

In Sifrei Zuta (1968), Lieberman advanced the view that this halakhic Midrash was in all likelihood finally edited by Bar Kappara in Lydda.

Other books of his were Sheki'in (1939), on Jewish legends, customs, and literary sources found in Karaite and Christian polemical writings, and Midreshei Teiman (1940), wherein he showed that the Yemenite Midrashim had preserved exegetical material which had been deliberately omitted by the rabbis.

Jacob Neusner, a leading scholar of the history of rabbinic Judaism, criticized the bulk of Lieberman's work as idiosyncratic in that it lacked a valid methodology and was prone to other serious shortcomings (see Sources below).

However, ten years earlier, in an article published shortly after his death, Lieberman strongly criticized Neusner's lack of scholarship in the latter's translation of three tractates of the Yerushalmi.

Lieberman insisted that all services at the Seminary's Stein Hall, where he prayed daily, have a mechitzah even though the great majority of Conservative synagogues did not.

Additionally, Lieberman saw to it that the Seminary synagogue in which he prayed used an Orthodox prayer book, rather than siddurim produced by the Rabbinical Assembly.

[9][better source needed] The Lieberman clause is a clause included in a ketubah (Jewish wedding document), created by and named after Saul Lieberman, that stipulates that divorce will be adjudicated by a modern bet din (rabbinic court) in order to prevent the problem of the agunah, a woman not allowed to remarry religiously because she had never been granted a religious divorce.

Among her publications were Robert Browning and Hebraism (1934), and an autobiographical chapter which was included in Thirteen Americans, Their Spiritual Autobiographies (1953), edited by Louis Finkelstein.