ImportanceDuring the COVID-19 pandemic, the prevalence and severity of intimate partner violence (IPV) increased. Associations between IPV and mental health symptoms and modifiable health factors early in the pandemic have yet to be explored.ObjectiveTo prospectively investigate the association of IPV with greater risk of mental health symptoms and adverse health factors during the COVID-19 pandemic in 3 cohorts of female participants.Design, Setting, and ParticipantsThis cohort study used observational data from 3 prospective, population-based, longitudinal cohorts in the US: the Nurses’ Health Study II, Growing Up Today Study, and Nurses’ Health Study 3. Data analyzed included baseline and follow-up survey responses about IPV experiences early in the pandemic (March-September 2020); mental health domains of depression, anxiety, and posttraumatic stress symptoms (PTSS); and modifiable health factors (May 2020-October 2021). Female participants (both health care professionals and non–health care workers) aged 21 to 60 years from the 3 cohorts were included in the full analytic sample.ExposuresExperience of IPV measured by the Relationship Assessment Tool and fear of partner.Main Outcomes and MeasuresMental health symptoms, including depression, anxiety, and PTSS, and modifiable health factors, including sleep duration, sleep quality, physical activity, alcohol use, and use of alcohol or other substances to cope with stress.ResultsThe full analytic sample included 13 597 female participants with a mean (SD) age of 44 (10.6) years. Accounting for sociodemographic factors and prepandemic mental health symptoms and correcting for multiple testing, experiencing IPV was associated with higher endorsement of depression (odds ratio [OR], 1.44; 95% CI, 1.38-1.50), anxiety (OR, 1.31; 95% CI, 1.26-1.36), and PTSS (OR, 1.22; 95% CI, 1.15-1.29) in random-effects meta-analyses across the 3 cohorts. The IPV experience was also associated with poorer sleep quality (OR, 1.21; 95% CI, 1.16-1.26), shorter sleep duration (OR, 1.13; 95% CI, 1.08-1.19), increased use of alcohol (OR, 1.10; 95% CI, 1.06-1.14), and use of alcohol or other substances to cope with stress (OR, 1.13; 95% CI, 1.08-1.18) across all cohorts as well as decreased physical activity (OR, 1.17; 95% CI, 1.09-1.26) in the Nurses’ Health Study II only.Conclusions and RelevanceResults of the study showed that IPV experiences at the start of the pandemic were associated with worse mental health symptoms and modifiable health factors for female participants younger than 60 years. Screening and interventions for IPV and related health factors are needed to prevent severe, long-term health consequences.