The increasing number of high-risk pregnancies has led to a greater emphasis on psychological well-being in nursing care. However, reducing depression does not automatically equate to increasing happiness. This study aimed to systematically examine the factors influencing happiness and depression among high-risk pregnant women in South Korea. This correlational, cross-sectional study was based on the ecological systems theory. In total, 152 high-risk pregnant women completed a self-report survey questionnaire available online or offline. Data were analyzed using hierarchical regression analysis. The first model (individual system) identified pregnancy stress and mindfulness as significant factors influencing both happiness and depression. The second model (microsystem) identified medical status at the time of the survey, maternal-fetal interaction, marital intimacy, and social support as additional significant factors influencing either happiness or depression. In the third model (mesosystem), maternal-fetal interaction and paternal-fetal attachment were no longer identified as significant factors. Although the fourth model (exosystem) did not identify community service as a significant factor, individual (pregnancy stress, mindfulness) and microsystem (marital intimacy) factors were found to influence happiness and depression. Medical status at the time of survey and social support were additional factors that influenced happiness, but not depression. These factors explained 51.2% and 55.5% of the variance in happiness and depression, respectively, among high-risk pregnant women. Different factors at the individual and microsystem levels affected happiness and depression among high-risk pregnant women. Hence, efforts to reduce depression among these women should be accompanied by efforts to actively promote happiness.