This study investigated associations of long-term romantic relationships with subjective well-being and its three components in emerging adulthood. In this developmental period emerging adults cope with an important developmental task of establishing a close and relatively lasting romantic relationship. A successfully resolved task associates with positive outcomes in individuals, including their subjective well-being. Personality traits and attachment styles were also considered in examining the link of romantic relationships with subjective well-being. Emerging adults (N = 491; 79% females), aged from 19 to 29 years, completed an online survey that comprised questionnaires of personality traits, attachment styles, and subjective well-being. The results indicated positive outcomes for individuals involved in a romantic relationship for at least 6 months, i.e. higher levels of overall subjective well-being and its private components (emotional and psychological well-being). Those in a relationship also tended to score higher in attachment security than their single peers. There were no differences between the singles and those in a relationship regarding their social well-being and the Big Five personality traits. The latter predicted overall subjective well-being and its three components most powerfully. Higher levels of both extraversion and conscientiousness and lower levels of neuroticism were statistically significantly associated with higher levels of subjective well-being and its components. The hierarchical regression analysis suggested that a relatively small amount of variance in subjective well-being (and its components) is explained by demographic variables. Personality traits substantially improved the prediction over and beyond demographics. Attachment styles further contributed a small, but statistically significant part to the variance explained above and beyond demographic variables and personality traits. However, the relationship status as a single predictor no longer played a significant role in overall subjective well-being and its components, except for emotional well-being. Emerging adults in a relationship reported on higher levels of emotional well-being. The study contributes to the understanding of factors contributing to subjective well-being in emerging adulthood.