Volcanoes, originating from deep-seated magmatic activity, serve as crucial conduits connecting Earth’s interior and surface. Volcanic eruptions, a primary manifestation of this connection, exert profound influence across Earth’s surface systems. Volcanic ash, a significant product of these eruptions, has long been a focal point of Earth science research due to its far-reaching impacts. However, the challenges associated with deep-sea sampling and a relative lack of interdisciplinary collaboration have hindered our understanding of how volcanic ash deposition affects the abyssal environment. Here, leveraging a combined geological and microbiological approach, we investigated sediments within the Kermadec Trench impacted by rhyolitic volcanic ash. Our findings demonstrate that iron availability is the primary driver of microbial community structure in these ash-influenced deep-sea sediments. The mantel test analysis further revealed that four key categories of iron-related functional genes involved in iron acquisition (heme transport, iron transport, and siderophore transport) and iron storage significantly shape the resident microbial communities. Furthermore, metagenomic binning yielded numerous refined metagenome-assembled genomes (MAGs) from these deep-sea sediments, all of which harbored iron-related functional genes. Viral metagenomic analysis suggests that viruses in these sediments do not directly influence abyssal prokaryote-mediated iron cycling through the carriage of iron-related auxiliary genes. Instead, viral lysis of iron-cycling prokaryotes appears to be a key regulatory mechanism. These results provide critical new data and insights into microbial iron cycling in the deep sea under the influence of volcanic ash deposition.