Previous research on pandemics and emergencies has shown that such events often widen health inequalities in society and have a greater impact on socially disadvantaged groups No review has so far looked at the impact of inequality factors on mental health outcomes during the novel coronavirus outbreak (COVID-19) The aim of the current review was therefore to assess the impact of inequality factors on mental health outcomes during COVID-19 After registration on PROSPERO, a systematic review was conducted for papers published up to July 31, 2020, using the databases Google Scholar, PsycINFO, PubMed (MEDLINE), and Web of Science The following inequality factors were considered: education, income, employment, occupation, material and social deprivation, age, immigrant status, sexual orientation, functional health, cultural/racial background, sex, gender, and place of residence Out of 1,931 references, 117 studies (300,061 participants) were included Female sex, being of a younger age, financial insecurity, lack of access to clear messaging/information about the pandemic, proximity to large infection sites, having existing physical and/or psychological health conditions, and being subjected to abuse/stigma because of one's identity as a member of an ethnic or sexual marginalized group predicted mental health inequalities More research is required on how inequality affects mental health in less studied vulnerable populations, such as ethnic, sexual, and gender marginalized participants, as well as how inequality factors interact to affect mental health in the long term Recommendations for researchers, mental health practitioners, and public health authorities for mitigating adverse mental health outcomes in vulnerable populations are outlined (PsycInfo Database Record (c) 2021 APA, all rights reserved) Abstract (French) Des recherches anterieures sur les pandemies et les urgences ont montre que de tels evenements augmentent souvent les inegalites en matiere de sante dans la societe et ont une incidence plus grave sur les groupes socialement defavorises A ce jour, aucune etude n'a examine l'incidence des facteurs d'inegalite sur les resultats en matiere de sante mentale lors de l'epidemie du nouveau coronavirus (COVID-19) L'objectif de la presente etude etait donc d'evaluer l'incidence des facteurs d'inegalite sur les resultats en matiere de sante mentale pendant la COVID-19 Apres inscription sur PROSPERO, un examen systematique a ete effectue pour les articles publies jusqu'au 31 juillet 2020, en utilisant les bases de donnees Google Scholar, PsycINFO, PubMed (MEDLINE) et Web of Science Les facteurs d'inegalite suivants ont ete pris en consideration : education, revenu, emploi, profession, privation materielle et sociale, age, statut d'immigrant, orientation sexuelle, sante fonctionnelle, origine culturelle/raciale, sexe, genre et lieu de residence Sur 1 931 references, 117 etudes (300 061 participants) ont ete incluses Le sexe feminin, le jeune age, l'insecurite financiere, le manque d'acces a des messages/renseignements clairs sur la pandemie, la proximite d'importants sites d'infection, les conditions de sante physique et/ou psychologique existantes et le fait d'etre victime d'abus/stigmatisation en raison de son identite en tant que membre d'un groupe ethnique ou sexuel marginalise ont permis de predire les inegalites en matiere de sante mentale Des recherches supplementaires sont necessaires sur la maniere dont les inegalites affectent la sante mentale dans les populations vulnerables moins etudiees, telles que les participants marginalises sur le plan ethnique, sexuel et sexospecifique, ainsi que sur la maniere dont les facteurs d'inegalite interagissent pour affecter la sante mentale a long terme Des recommandations sont formulees a l'intention des chercheurs, des praticiens de la sante mentale et des autorites de sante publique pour attenuer les effets nefastes sur la sante mentale des populations vulnerables (PsycInfo Database Record (c) 2021 APA, all rights reserved) Impact Statement Public Significance Statement-The findings of this review suggest that several inequality factors, such as female sex, younger age, financial insecurity, having existing chronic health conditions, and being in an ethnic or sexual marginalized group predict worse mental health outcomes during the ongoing COVID-19 pandemic There is an urgent need for mental health services to support vulnerable populations at this time, to reduce mental health inequalities and improve long-term psychological functioning (PsycInfo Database Record (c) 2021 APA, all rights reserved)