This study examined the impact of social media marketing on online purchase intention, with brand attachment, brand trust, and brand equity acting as mediating factors. The problem addressed in this research is the lack of understanding regarding the reasons for low adoption of online shopping in Iran despite the increasing popularity of the internet, and the originality lies in exploring the factors and proposing and testing a conceptual model that influence Iranian customers’ decision to buy online. To conduct an empirical case study, we selected Digikala, the largest online two-sided marketplace platform in Iran. To gather data from a representative sample of Digikala customers, a simple random sampling method was utilized. An online survey questionnaire was administered to 363 participants, ensuring a diverse range of respondents were included in the study. A partial least squares method was used to analyze the data using the structural equation modelling (SEM) method by SmartPLS software. The results of the research study demonstrated that social media marketing creates positive changes in brand equity, customer attachment to the brand, brand trust, and online purchase intent over time. Online purchase intention, brand trust, and customer brand attachment were positively influenced by brand equity. The level of customer brand attachment affected brand trust and online purchase intent in a positive way. An increase in brand trust led to a significant increase in online purchase intentions. An online purchase intention, customer brand attachment, and brand trust of a brand were influenced positively by brand equity during social media marketing. Social media marketing impacted online purchase intentions positively and significantly through customer brand attachment. Social media marketing improved online purchase intentions when brand trust is positive and significant. Several factors contributed to the effect of social media marketing on online purchase intentions, including brand trust. This leads us to conclude that social media marketing enhances online purchase intent through the creation of brand attachments, brand trust, and brand equity among customers.