Interleukin 1β (IL-1β) is a potent proinflammatory factor during viral infection. Its production is tightly controlled by transcription of Il1b dependent on the transcription factor NF-κB and subsequent processing of pro-IL-1β by an inflammasome. However, the sensors and mechanisms that facilitate RNA virus–induced production of IL-1β are not well defined. Here we report a dual role for the RNA helicase RIG-I in RNA virus–induced proinflammatory responses. Whereas RIG-I-mediated activation of NF-κB required the signaling adaptor MAVS and a complex of the adaptors CARD9 and Bcl-10, RIG-I also bound to the adaptor ASC to trigger caspase-1-dependent inflammasome activation by a mechanism independent of MAVS, CARD9 and the Nod-like receptor protein NLRP3. Our results identify the CARD9–Bcl-10 module as an essential component of the RIG-I-dependent proinflammatory response and establish RIG-I as a sensor able to activate the inflammasome in response to certain RNA viruses.