Advances in digital technology have led to large amounts of personal data being recorded and retained by industry, constituting an invaluable asset to both governmental and private organizations. The implementation of the General Data Protection Regulation in the EU, including the UK, fundamentally reshaped how data is handled across every sector. It enables the general public to access data collected about them by organisations, opening up the possibility of this data being used for research that benefits the public; for example, to uncover lifestyle causes of health outcomes. A significant barrier for using this commercial data for academic research is the lack of publicly acceptable research frameworks. Data donation - an act of active consent of an individual to donate their personal data for research - could enable the use of commercial data for societal benefit. However, it is not clear which motives, if any, would drive people to donate their personal data. In this paper we present the results of a large-scale survey (N = 1,300) that studied intentions and reasons to donate personal data. We found that over half of individuals are willing to donate their personal data for research that could benefit the wider general public. We identified three distinct reasons to donate personal data: an opportunity to achieve self-benefit, prosocial motive to serve society, and the need to understand the purpose of data donation. We developed a questionnaire to measure those three reasons and provided further evidence on the validity of the scales. Our results demonstrate that these motivations predict people’s intentions to donate personal data over and above generic altruistic motives and relevant personality traits. We show that a prosocial motive to serve society is the strongest predictor of the intention to donate personal data, while understanding the purpose of data donation also positively predicting the intentions to donate personal data. In contrast, self-serving motives show a negative association with intentions to donate personal data. The findings presented here inform the ethical use of commercially collected personal data for academic research for public good.