This comprehensive systematic review delves into the use of Large Language Models (LLMs) in the field of digital marketing, focusing on their evolution, influence, and current practical applications. Employing a meticulous approach to analyze the scholarly literature in Scopus and Web of Science databases, this review ranges from basic implementations of LLMs to their more sophisticated applications in the marketing field. In particular, models such as ChatGPT have transformed the existing customer-salesperson relationship, providing accurate and personalized real-time responses that have significantly improved the customer experience and the effectiveness of marketing strategies. The review focuses on three main areas: the integration of LLMs into chatbots, which has improved the user experience and boosted conversion and retention rates in e-commerce; adaptive content development to optimize social media advertising campaigns; and predictive analytics, which streamlines strategic decision-making by analyzing historical and real-time data. These advances have enabled marketers to design more informed and personalized strategies, refine campaigns and promotions, and improve the overall customer experience.