Spin defects in semiconductors are attractive candidates for a qubit, which is an essential element for quantum technologies, such as quantum communication, computing, and sensing. As a host of spin defects, silicon carbide (SiC) is promising owing to its wide bandgap, well-established crystal growth, doping control, and process technologies. Various spin defects in SiC including silicon vacancy (V_Si) and nitrogen-vacancy (N_CV_Si) complex were already reported. Recently, a theoretical study predicted the neutral oxygen-vacancy (O_CV_Si) complex as a candidate qubit with a high-spin ground state (S = 1) with near-infrared photoemission (1004–1117 nm). Its calculated high Debye-Waller factor (13.4%) is favorable for a spin-to-photon interface. However, a systematic study on other types of oxygen-related defects is still lacking. In this study, we systematically investigated the stability, structure, energy levels, and spin properties of oxygen-related defects in 4H-SiC taking the relevant charge states into account.