In the high-paced, uncertain, and resource-constrained environment of software startups, achieving product–market fit and acquiring initial customers are critical yet challenging tasks. These challenges are often exacerbated by the absence of strategic planning, inefficient requirements selection processes, inadequate resource allocation, and insufficient market research, leading to an alarming 63% failure rate among software startups. The Product Manager (PM), responsible for product strategy, planning, and results monitoring, plays a pivotal role in navigating these complexities; however, the PM role is often undervalued and lacks a universally accepted definition. This study aims to enhance the understanding of the PM's role within software startups by conducting a comprehensive Systematic Literature Review (SLR). Employing a rigorous selection methodology, we reviewed 134 studies and identified 662 distinct PM tasks across 122 activities. Notably, only 7 studies (5.73%) specifically addressed the software startup context, revealing a substantial gap in the literature. Our findings indicate that while product planning and requirements prioritization are dominant topics, many critical activities remain underrepresented, underscoring the need for targeted research in these areas. By addressing the unique challenges faced by software startups, we pave the way for more targeted and effective PM strategies. Future research should consider adopting mixed-method approaches to deepen the understanding of PM practices and investigate underexplored areas such as go-to-market strategies, roadmap creation, and requirements selection within the startup context.