Birth order has long been viewed as an important influence on personality, behavior, and social development. However, its specific link to emotional intelligence (EI) and the quality of interpersonal relationships has received far less attention. This study explores how emotional intelligence varies among first-born, middle-born, last-born, and only children, focusing on key areas such as self-awareness, self-regulation, empathy, and social skills. It also examines how these differences shape relationships within families, among peers, and in romantic contexts.

A mixed-method approach was adopted to capture a broad and detailed picture of these dynamics. Data were gathered from 600 adults aged 18–45 drawn from diverse socioeconomic and cultural backgrounds. Emotional intelligence was assessed using the Schutte Self-Report Emotional Intelligence Test (SSEIT), while relationship quality was measured through validated tools covering trust, communication, conflict resolution, and satisfaction.

The quantitative analyses, which included ANOVA and regression techniques, revealed significant differences across birth-order groups. Later-born participants tended to score higher in peer-related empathy, while first-borns demonstrated stronger self-regulation skills. In-depth interviews provided further insight into how family structures, parental expectations, and sibling dynamics help shape these outcomes.

These findings carry valuable implications for educators, mental health professionals, and organizational leaders. By understanding how birth order relates to emotional competencies, interventions in areas such as social skills development, conflict management, and team building can be better tailored to individual needs. Beyond its practical applications, the study adds to the growing body of theoretical work connecting birth order with emotional development and relationship outcomes. It highlights the importance of viewing individual differences through a nuanced lens that considers both personal and contextual factors in shaping emotional and social functioning.