Background: Contact tracing is a key control measure in the response to the COVID-19 pandemic. While quantitative research has been conducted on the psychological impact of the pandemic on other frontline healthcare workers, none has explored the impact on contact tracing staff. Methods: A longitudinal study was conducted using two repeated measures with contact tracing staff employed in Ireland during the COVID-19 pandemic using two-tailed independent samples t tests and exploratory linear mixed models. Results: The study sample included 137 contact tracers in March 2021 (T1) and 218 in September 2021 (T3). There was an increase from T1 to T3 in burnout related exhaustion (p < 0·001), post-traumatic stress disorder (PTSD) symptom scores (p < 0·001), mental distress (p < 0·01), perceived stress (p < 0·001) and tension and pressure (p < 0·001). In those aged 18–30, there was an increase in exhaustion related burnout (p < 0·01), PTSD symptoms (p < 0·05), and tension and pressure scores (p < 0·05). Additionally, participants with a background in healthcare showed an increase in PTSD symptom scores by T3 (p < 0·001), reaching mean scores equivalent to those of participants who did not have a background in healthcare. Conclusions: Contact tracing staff working during the COVID-19 pandemic experienced an increase in adverse psychological outcomes. These findings highlight a need for further research on psychological supports required by contact tracing staff with differing demographic profiles. [ABSTRACT FROM AUTHOR]