This is a protocol for a systematic review and meta-analysis of research on mental health outcomes of abortion. Does abortion increase the risk of adverse mental health outcomes? That is the central question for this review. Our review aims to inform policy and practice by locating, critically appraising, and synthesizing empirical evidence on associations between abortion and subsequent mental health outcomes. Given the controversies surrounding this topic and the complex social, political, legal, and ideological contexts in which research and reviews on abortion are conducted, it is especially important to conduct this systematic review and meta-analysis with comprehensive, rigorous, unbiased, and transparent methods. We will include a variety of study designs to enhance understanding of studies methodological strengths and weaknesses and to identify potential explanations for conflicting results. We will follow open science principles, providing access to our methods, measures, and results, and making data available for re-analysis.