Research on bystander intervention (BI) during public harassment, that is, intrusive and intimidating (sexual) behaviors in public spaces, remains scarce, creating knowledge gaps regarding its frequency, influencing factors, and impact. This study addresses these gaps by examining BI experiences among an age-diverse sample (16–82 years) living in 10 Belgian municipalities, based on 541 reports collected through an online platform in 2023. Moreover, this study examines BI from two perspectives: receiving help during a specific incident and offering help oneself. BI occurred in only 28% of public harassment incidents with witnesses present, and around half of respondents had ever intervened. Given that prior research on violent conflicts reports much higher intervention rates, this low intervention rate suggests that harassment is perceived as less dangerous and supports the need to raise awareness about its harms. Intervention was more likely when bystanders knew the victim, underlining the potential of fostering a stronger sense of community to encourage intervention. Finally, this study found that victims were significantly more likely to report perceived support when bystanders intervened, highlighting the value of promoting BI.