A two-phase mixed-methods study evaluates the Gwent Test Trace Protect Services (GTTPS), serving a population of approx. 600,000 in Southeast Wales. The evaluation focuses on the contact tracing element and incident management (regional cell) elements of Test Trace Protect (TTP) rather than the test or protect elements. The project aims at (1) understanding how organisational structures and the dissemination of information developed around a specific need during the early phase of the GTTPS, describing the initial set-up of the GTTPS in May 2020, (2) investigating when governance structures were established and how they evolved, (3) comprehending how the design deviated from its initial set-up, proactively adapting and further evolving according to demand, (4) analysing the robustness of the emergent systems, and (5) identifying the specific learning for future TTP service developments or other Public Health partnerships (e.g., around organisational culture and working climate). Research findings reveal the success factors of this award-winning integrated service, contribute to the evidence base on developing a contact tracing service at a population scale, and include workforce recommendations to enhance the resilience of the service. Until August 2021, the GTTPS exhibited a 98% success rate, i.e., the service sucessfully followed up 98% of the contacts within 24 hours of being identified as a close contact of a positive case. The surge of the Delta and Omicron variants combined with reducing restrictions on people’s activity affected cases and the service’s success rate. Overall, in 2021, the GTTPS successfully followed up 81% of 101,743 positive cases and 81% of 164,926 associated contacts (21,951 of those tested positive).