Artificial intelligence (AI) is increasingly integrated into scientific discovery processes, such as protein design, gene analysis, and materials research, significantly enhancing the efficiency of discoveries in these fields. While much recent literature emphasizes fully automated pipelines, it is crucial to acknowledge that scientific discovery is inherently a creative and high-stakes endeavor. Therefore, it relies heavily on human expertise for judgment and guidance, especially in the face of uncertainty. Despite rapid growth in human-in-the-loop and collaborative systems, the field lacks a unifying survey that explains how humans and AI actually collaborate across the scientific discovery life-cycle. In this paper, we present a systematic review of human–AI (HAI) collaboration for scientific discovery. Specifically, we have identified four representative roles of humans and AI. Using this lens, we then distill common HAI collaboration patterns across three distinct stages in the scientific discovery process (i.e., observation, hypothesis, and experiment). Finally, we identify key gaps in existing approaches and outline future research directions for developing trustworthy, role-aware human–AI systems in scientific discovery.