The 53Co 19/2- isomer at 3174 keV is a special metastable state that is the first proton emitter discovered. It is also important in nuclear astrophysics. In this paper, we present ab initio calculations that provide a comprehensive understanding of the structure, beta decay, and formation mechanism of the isomer. The calculations were performed by the valence-space in-medium similarity renormalization group based on chiral effective field theory (chi EFT) nuclear forces with the three-nucleon force included. It is found that the three-nucleon force plays a crucial role in the formation of the 19/2- isomer. The 53mCo (19/2-) lifetime is mainly determined by the beta decay into 53mFe (19/2-), which was calculated with a quenching factor obtained by considering the chi EFT two-body currents.