Feminist data activism aims to safeguard the interests and rights of marginalised groups. This paper examines how feminist data activists critically and creatively engage with digital data and related technologies, thereby also contributing to grassroots technology innovation. Conceptually, it draws on the notion of data solidarity. While this concept has been mainly explored in data governance frameworks and ethics, this paper analyses civic and academic data activism – acknowledging that the lines between civic vis-à-vis academic practices are blurring. It starts from the question how data solidarity may co-shape feminist data activism. Methodologically, it pursues a cultural media studies approach and comparatively analyses three cases. The paper argues that data solidarity is insightful for understanding how the interplay, including tensions, between individual autonomy and collective control may facilitate (co-)creation of data with public value.