AbstractIntegrating photoactive proteins with synthetic nanomaterials holds great promise in developing optoelectronic devices whereby light, captured by a antenna protein, is converted to a modulated electrical response. The protein–nanomaterial interface is critical to defining optoelectronic properties; successful integration of bionanohybrids requires control over protein attachment site and a detailed understanding of its impact on device performance. Here, the first single‐walled carbon nanotube (SWCNT) bio‐optoelectronic transistor enabled by the site‐specific direct interfacing with a green fluorescent protein (GFP) via genetically encoded phenyl azide photochemistry is reported. The electrical behavior of individual semiconducting SWCNTs depends on the protein residue coupling site and provides the basis to design eco‐friendly phototransistors and optoelectronic memory. Attachment at one GFP residue proximal to the chromophore produces a wavelength‐specific phototransistor. The bio‐transistor can be switched off in less than 38 s with responsivity up to 7 × 103 A W−1 at 470 nm. Attachment via a second residue distal to the chromophore generates optoelectronic memory that show rapid and reproducible conductivity switching with up to 15‐fold modulation that is restored on the application of a gate voltage. Therefore, photoactive proteins, especially GFP, can be realized as a key material for novel single‐molecule electronic and photonic devices.