Seabirds have been the messengers of marine plastics pollution since the 1950s, not long after plastics began to be commercially manufactured. In the decades since, a number of multilateral agreements have emerged to address marine plastics pollution that have been informed by research and monitoring on plastic ingestion in seabirds. Seabirds continue to serve as effective monitors for plastics pollution in the oceans, and increasingly of the chemical contamination from the marine environment as plastic additives and chemicals can adsorb and accumulate in seabirds’ tissues. Plastics pollution has far-reaching ecological impacts, but the motivation for addressing the issue has escalated rapidly at the international level. Seabirds are also the most globally threatened group of birds and require concerted conservation actions to mitigate population declines from multiple pressures. However, most policy mechanisms focus on the monitoring and mitigation of anthropogenically induced stressors, using seabird data, and often fail to include mechanisms to conserve the messengers. In this review, we discuss how research on the impacts of plastics on seabirds is used to inform policy and highlight the competing interests of monitoring and conservation that emerge from this approach. Finally, we discuss policy opportunities to ensure seabirds can continue to be the indicators of ocean health and simultaneously achieve conservation goals.