Sociality is the inclination of an individual towards group living. The social structure within a group can be expressed through social networks, which display the mutual interactions among individuals within a population. Within the social network, we can quantify the social network metrics of an individual, such as the number, strength, and stability of social ties, or the centrality of the individual within the network. The goal of this paper is to determine whether social network metrics in mammals affect the fitness of an individual (through survival and reproduction). The research was conducted in the form of a systematic review and meta-analysis. A systematic collection of previously published literature (scientific articles) in English was gathered, followed by screening of the literature and data extraction from relevant articles. Statistical analysis in the form of a meta-analysis was conducted on the extracted data. The research results have shown a significant positive impact of social network metrics on the fitness of individuals. Additionally, social network metrics have a statistically significant impact on the reproduction of the individual, while their impact on survival was not statistically significant. A greater impact was observed in females compared to males, in juveniles and adults compared to other age groups, and in associations between individuals of the same sex compared to associations with the opposite sex. The impact on fitness was also dependent on the type of social network metrics, level of sociality, and mating system. There are numerous 'gaps in knowledge' in the literature, so the emphasis in future work should be on the diversity of studies.