In the context of international investment disputes, this paper investigates how arbitrator team characteristics affect team performance in solving disputes between a host country and a foreign investor. Our data include 277 judgments issued by arbitrator teams at the International Centre for Settlement of Investment Disputes at the World Bank from 1972 to 2018. The time to resolution and the quality of the final judgment, as measured by the requirement of a follow-on proceeding to rectify mistakes, are used to measure the team performance. We consider both biographical and professional characteristics of the arbitrators as determinants of the team performance. We find that mixed gender teams and previous team member’s collaborations increase the time to resolution contrary to team members’ experience and diversity in the professional background that decrease it. None of the team characteristics considered has an impact on the quality of the final judgment. Our findings talk to the current policy debate on the reform of the international investment arbitration system aiming to increase its effectiveness and transparency.