Upon detection of foreign nucleic acid, the cytosolic RNA receptor, retinoic acid inducible gene-I (RIG-I) initiates a cascade of signalling pathways leading to type I interferon production, to execute direct antiviral effects. On a structural level, the molecular movements that are required in order for the N-terminal caspase activation and recruitment domains (CARDs) of RIG-I to interact with the down stream signalling partner, interferon promoter stimulator-1 (IPS-1), are yet to be elucidated. Here, we use size-exclusion chromatography-coupled small angle X-ray scattering to show the in-solution structure of RIG-I in complex with immunostimulatory RNA, detailing the stoichiometry, the movement of the individual domains and extension of the molecule. The characterisation of the domain rearrangement of RIG-I in complex with immunostimulatory RNA also reveals the exposure of regions of RIG-I that are potentially targeted by immune evasion proteins produced by viruses, in addition to exposure of specific amino acids that are involved in regulation of the activity of RIG-I in triggering the innate immune response.