Coronavirus disease (COVID-19) outbreaks on board cruise ships early in the pandemic highlighted gaps worldwide in public health emergency contingency plans (PHECPs) for responding to unknown threats. To restart cruise operations in 2021 and respond to potential COVID-19 outbreaks, a major tourist-based Greek island port (Port A) developed a COVID-19 PHECP. We assessed plan effectiveness by reviewing epidemiological data and monitoring outcomes, followed by an intra-action review (IAR) analyzing three event responses. From May to December 2021, 118 calls from 23 cruise ships with 119,930 passengers were recorded, with 29 COVID-19 cases in 11 cruises on board 7 ships. No outbreak was recorded during the study period. Strengths of the introduced PHECP included commitment of senior management; a core multi-disciplinary team of local authorities/ship agents involved in design and execution; interoperability agreements for port and ships’ PHECPs; cruise industry commitment to compliance; and pre-existing scenarios considering capacity needs. Central government coordination for preparedness planning at local ports is essential for successful responses. Monitoring local and country level response capacities is critical to inform planning, risk assessment, and decision-making. Immediately recording ports’ response actions provides the basis to capture lessons and improve contingency plans. To facilitate communication and common response protocols between European and non-European ports, IARs should be conducted between countries.