Son of Rabbi Yitzchak, the rabbi of Slavuta, he was a descendant of Rabbi Shimshon of Ostropole. He was a disciple of the Maggid of Mezritch , Rabbi Pinchas of Koretz and a close friend of Rabbi Baruch of Medzhiboz.
Rabbi Yaacov Shimshon of Shepetovka was a great halachic authority whose considerable erudition earned him respect and recognition in rabbinic circles. He is quoted in Zera Efraim by R' Efrayim Zalman Margulies.
He was assigned the formidable task of expounding chassidic doctrine to such rabbinical authorities as R' Yechezkel Landau of Prague, R' Yeshaaya Yehuda Loeb Berlin, and R' Efrayim Zalman Margulies of Brody. These rabbis were opposed to to the chassdic movement of the Baal Shem Tov.
He succeeded his father as rabbi in Shepetovka, but in 1799 he settled in Teveria (Israel) where he met Rabbi Nachman of Breslov while he was on his journey in Israel. It was a great joy for Rabbi Yaacov Shimshon to meet Rabbi Nachman , he made a meal in his honor and rejoiced exceedingly with him, speaking privately with him for a long while.
Rabbi Yaakov Shimshon traveled as an emissary on behalf of the chasidic settlers in Israel.
May the merit of the tzaddik Rabbi Yaakov Shimshon of Shepetovka protect us all, Amen.