<p>Worldwide volunteering plays a key role in helping people in need. Volunteering in prisons contributes to the rehabilitation of inmates during their time in jail and their reintegration back in society. However, little is known about the general population’s attitudes towards volunteering in prison. We conducted a content analysis of publicly available data on Twitter from 1st January 2017 to 31st October 2022. The codebook used consisted of classifying tweets according to the type of content and type of user. The number of retweets and likes generated by each tweet was analysed as an indicator of user interest; the type of content was investigated per continent; an emotion analysis was also conducted. A total of 101,349 tweets in English and 5,001 tweets in Portuguese were considered classifiable. ‘Volunteering as an alternative to jail time or reduced sentence time’ was the topic that generated most tweets and ‘Volunteering impact’ was the topic that generated the least in both languages. America was the continent with more tweets; in both languages, the average number of likes per tweet was higher than the average number of retweets. Angry emotions were the most expressed by users. This study is the first application of social media research to investigate the public discourse about volunteering in prisons. Overall, public attitudes towards volunteering in prisons are negative. Continued efforts are required to raise awareness about volunteering in prisons.</p>