This study examines the impact of investor sentiment and market sentiment on overreaction in Europe and USA markets before and during COVID-19. The investor sentiment is calculated by the standard deviation, realized volatility, Parkinson’s estimator and Garman and Klass’s estimator. The market sentiment is measured by Business Confidence Index, Consumer Confidence Index, Labour Force Survey, Leading Index and Monetary Aggregates. The results of this study show that investor and market sentiments are correlated to stock return before COVID-19. Nonetheless, realized volatility is the only investor sentiment that is significant with the emergence of COVID-19. It shows that investors rely on the previous day’s stock prices to trade under market uncertainty. Market sentiment is observed to be insignificant in the pandemic. Furthermore, the existence of overreaction is detected in European portfolios but no evidence of overreaction is shown in the USA during pre-COVID-19. Surprisingly, overreaction is observed in Europe and USA markets in the pandemic. The USA market has a higher overreaction tendency than Europe. The results of this study assist academicians, practitioners and investors in understanding and creating awareness of the existence of market overreaction and its determinants before and during COVID-19.