As a benthic filter feeder of estuaries, the immune system of oysters provides one of the best models for studying the genetic and molecular basis of the innate immune pathway in marine invertebrates and examining the influence of environmental factors on the immune system. Here, the molecular function of molluscan TANK-binding kinase-1 (TBK1) (which we named CgTBK1) was studied in the Pacific oyster, Crassostrea gigas. Compared with known TBK1 proteins in other model organisms, CgTBK1 contains a conserved S-TKc domain and a coiled coil domain at the N- and C-terminals but lacks an important ubiquitin domain. Quantitative real-time PCR analysis revealed that the expression level of CgTBK1 was ubiquitous in all selected tissues, with highest expression in the gills. CgTBK1 expression was significantly upregulated in response to infections with Vibrio alginolyticus, ostreid herpesvirus 1 (OsHV-1 reference strain and μvar), and polyinosinic:polycytidylic acid sodium salt, suggesting its broad function in immune response. Subcellular localization showed the presence of CgTBK1 in the cytoplasm of HeLa cells, suggesting its potential function as the signal transducer between the receptor and transcription factor. We further demonstrated that CgTBK1 interacted with CgSTING in HEK293T cells, providing evidence that CgTBK1 could be activated by direct binding to CgSTING. In summary, we characterized the TBK1 gene in C. gigas and demonstrated its role in the innate immune response to pathogen infections.