Background and objective: Televised political debates offer voters the opportunity to compare their options. However, the effects of debates on voters remains unclear. As the criteria for evaluating candidates is increasingly based on non-political characteristics such as candidates’ image, our aim was to evaluate the effect of debates on voters' perceptions of candidates' likeability.

Methods: We employed a within subject’s pretest/postest design to monitor participants before and after the debate between the leaders of the two main Portuguese parties before the 2019 legislative elections. Before and after the debate broadcast, participants completed surveys focusing on the campaign and the debate itself. A statistical pipeline consisting of frequentist statistics and Bayesian statistics was applied to isolate debate effects.

Results: The debate influenced the perceived likability of both candidates. Both candidates were more positively evaluated by viewers in terms of perceived likeability after the debate. Candidates’ likeability before the debate and the candidates' performance during the event were significant predictors of the candidate's likeability after the debate.

Conclusions: By appearing live on debates, candidates not only gain notoriety, but they are more positively evaluated by viewers. These effects are based on the perceived likeability of the candidates before the debate and their performance during the debate itself. This study contributes to the theoretical and methodological literature on televised political debates and supports the claim that these events can shift voters’ attitudes.