Gesmundo was appointed to the Supreme Court as its 178th magistrate on August 14, 2017.

He was the chairperson of the technical working group for the Revision of the Law Student Practice Rule, and the Organizing Committee for the 2019 Legal Education Summit. He was the vice chairperson of the special committee for the rules of procedure for admiralty cases, special committee for the rules on inspection (under the Philippine Competition Act), the sub-committee for the revision of the 1997 Rules of Civil Procedure, the special committee on the rules of procedure in election contests before the First Level Courts.