Social relationships are of great importance across the lifespan, particularly during the formative years bracketing childhood. Various studies have researched the impact of peers and parent-child alliances on romantic relationships, but the influence of sibling relationships remains somewhat neglected. A study conducted by Statistics New Zealand (2020) reported that six in ten families in New Zealand have children, with approximately 60% of these households with more than one child. Siblings are known to spend a significant amount of time with each other compared to other relationships. If parent-child bonds can impact the quality of one’s romantic relationships, the probability of sibling attachments being influential is high. As a result, this research examined whether parental attachment or sibling attachment influences the quality of later life romantic relationships. A total of 91 undergraduate students at the Auckland University of Technology, aged 18 years and above, completed an anonymous questionnaire that explored attachment with their mother, father, and sibling during childhood and the quality of their romantic relationships in adulthood. The findings revealed that sibling attachment was the best predictor of romantic relationship quality as maternal and paternal attachment, both, found non-significant relationships with this outcome variable. Interestingly, sibling warmth during childhood reduced, whilst sibling conflict strengthened, the quality of later romantic relationships. Additionally, ageing individuals reported experiencing dissatisfaction with a romantic partner, whereas the increasing age of a sibling was associated with better romantic outcomes in later life. Some shortcomings of this research included a small sample size and the inability to assess sibling placement; however, suggested future research directions have been discussed. Essentially, the current research helps inform understanding of how early life attachments with different family members can influence the quality of one’s romantic relationships. It is hoped the efforts of this research will facilitate an inspiring direction for future studies on the topic of parental and sibling attachment.