Online petitions have become a widespread vehicle for contemporary political participation. While research tends to focus on individual factors for potential petitioners that influence signing, less attention has been paid to the influence of the actual text of petitions. This paper uses data from an original web-based survey experiment in Australia and Germany to test the influence of content factors: narratives (i.e., stories based on individual experiences and emotions) and popularity cues (i.e., high numbers of signatures) across two issues: climate change and welfare policy. We find that narratives within petition texts involve readers through the mechanism of transportation and motivate them to sign petitions, as do popularity cues. The effects of narratives were found across both countries but tended to be stronger in Germany than in Australia. We argue that our novel framework can be used for future research on how the presentation of issues shape contemporary political participation.