Halogen dopants in ZnSe have been a research focus for quantum applications utilizing excitonic emissions, wherein point defects play a critical role. To provide a full first-principles perspective on the defect chemistries of halogen-doped ZnSe, Cl- and F-doped ZnSe were explored via hybrid functional density functional theory calculations involving all possible isolated defects and defect-defect complexes. Cl and F both exhibit more complicated defect chemistries than just forming a shallow substitutional donor on the Se site. For Cl, the complex of Cl substituting for Se with a neighboring Zn vacancy was also found to be prevalent. For F, its interstitial in the Zn tetrahedron was found to be stable in addition to the complex of such interstitial with an adjacent F atom substituting for Se. The explicitly simulated emission photoluminescence lineshapes of the self-activated centers exhibited both a peak value and a broad line width consistent with the experiment.