Introduction: The COVID-19 pandemic increased the demand for mental-health services worldwide. Consequently, it also increased the length of the waitlists for mental-health services, putting a strain on adult mental-health services (AMHS) and the healthcare professionals dealing with these lists. There is little research about how psychologists managed waitlist practices, e.g., scheduling screening appointments, determining clients’ availability in an offered appointment, providing evidence-based bibliotherapy, or using priority waiting scales. It remains unclear what their experiences were with these practices and how effective these practices were during the pandemic. Method: The current convergent, concurrent mixed-method study investigated waitlist-management practices, synthesizing quantitative and qualitative data from an online survey (n = 20 participants) applied in two local AMHS in Ireland. Results: The most common practices used by psychologists were opt-in systems, maintaining regular contact with clients, informing them about the waiting time, and providing evidence-based bibliotherapy. Screening was the least-used practice. The qualitative analysis highlights the emotional burden psychologists experienced from the use of waitlist practices, particularly when they had to inform the client of the waiting time or put a client back onto a waitlist. Discussion: Psychologists reported a lack of resources and increases in administrative workload as barriers to implementing practices. Managerial, organizational, and policy-based recommendations are proposed.