Rav Nissim studied at the Kairouan Yeshiva, initially under his father, Jacob ben Nissim, who had studied under Hai ben Sherira and then Chushiel, who succeeded as head of the yeshiva.
Nissim himself later became head of the yeshiva; in this capacity he is closely associated with Chananel ben Chushiel.
The commentary Sefer mafteaḥ le-manʻ ūlei ha-talmūd (Hebrew: "The book of the key to unlocking the Talmud"; often, simply ha-Mafteach, (The Key), linked here) is essentially a Talmudic cross-reference.
Nissim did not confine himself to quoting references, he also discusses these in connection with the text; this work is thus also a commentary.
Nissim also wrote other works, some of which have been lost, but which are quoted by later sages: R. Nissim appears as a character in A Delightful Compendium of Consolation: A Fabulous Tale of Romance, Adventure and Faith in the Medieval Mediterranean, a novel by Burton Visotzky.