Abstract Background Regionally-specific approaches to primary mental health service provision through Primary Health Networks (PHNs) have been a feature of recent national mental health reforms. No previous studies have been conducted to investigate local patterns of primary mental health care (PMHC) services in Western Sydney. This study is designed to (i) understand the socio-demographic and economic profiles (ii) examine the inequalities of service access, and (iii) investigate the service utilisation patterns, among those referred to PMHC services in Western Sydney, Australia. Methods This study used routinely collected PMHC data (2005–2018), population-level general practice and Medicare rebates data (2013–2018) related to mental health conditions, for the population catchment of the Western Sydney PHN. Sex- and age-specific PMHC referrals were examined by socio-demographic, diagnostic, referral- and service-level factors, and age-specific referrals to PMHC services as a percentage of total mental health encounters were investigated. Results There were 27,897 referrals received for 20,507 clients, of which, 79.19% referrals resulted in follow-up services with 138,154 sessions. Overall, 60.09% clients were female, and median age was 31 years with interquartile ranged 16–46 years. Anxiety and depression were the predominant mental health condition, and 9.88% referred for suicidal risk. Over two-thirds of referrals started treatments during the first month of the referral and 95.1% of the total sessions were delivered by face to face. The younger age group (0–24) had greater referral opportunities as a percentage of total visits to a general practitioner and Medicare rebates, however demonstrating poor attendance rates with reduced average sessions per referral compared with older adults. Conclusion Children and young adults were more likely to be referred to PMHC services than older adults, but were less likely to attend services. Further research is needed to identify the strategies to address these differences in access to PMHC services to optimise the effectiveness of services.