Background Stress experienced in a marriage or committed relationship may be associated with worse patient‐reported outcomes after acute myocardial infarction (AMI), but little is known about this association in young adults (≤55 years) with AMI. Methods and Results We used data from VIRGO (Variation in Recovery: Role of Gender on Outcomes of Young AMI Patients), an observational cohort study that enrolled individuals aged 18 to 55 years with AMI (2008–2012). Marital stress was self‐reported 1 month after AMI using the Stockholm Marital Stress Scale (categorized as absent/mild, moderate, and severe). Outcomes were physical/mental health (Short Form‐12 ) , generic health status (EuroQol‐5 Dimensions), cardiac‐specific quality of life and angina (Seattle Angina Questionnaire), depressive symptoms (Patient Health Questionnaire‐9), and all‐cause readmission 1 year after AMI. Regression models were sequentially adjusted for baseline health, demographics (sex, age, race or ethnicity), and socioeconomic factors (education, income, employment, and insurance). Sex and marital stress interaction was also tested. Among 1593 married/partnered participants, 576 (36.2%) reported severe marital stress, which was more common in female than male participants (39.4% versus 30.4%, P =0.001). Severe marital stress was significantly associated with worse mental health (beta=−2.13, SE=0.75, P =0.004), generic health status (beta=−3.87, SE=1.46, P =0.008), cardiac‐specific quality of life (beta=−6.41, SE=1.65, P <0.001), and greater odds of angina (odds ratio [OR], 1.49 [95% CI, 1.06–2.10], P =0.023) and all‐cause readmissions (OR, 1.45 [95% CI, 1.04–2.00], P =0.006), after adjusting for baseline health, demographics, and socioeconomic factors. These associations were similar across sexes ( P ‐interaction all >0.05). Conclusions The association between marital stress and worse 1‐year health outcomes was statistically significant in young patients with AMI, suggesting a need for routine screening and the creation of interventions to support patients with stress recovering from an AMI.