Irreversible monoamine oxidase inhibitor (MAOI) antidepressants have significant efficacy in treatment-resistant unipolar depression, but in some instances patients may not achieve remission. Among the adjunctive and augmentation strategies, certain second-generation antipsychotics (SGAs) have approval for inadequate responders to antidepressant therapy, including aripiprazole, brexpiprazole, and quetiapine, with lurasidone and the olanzapine/fluoxetine combination indicated for bipolar depression. Clinicians may eschew SGA options in part due to the limited literature on SGA–MAOI combinations, with only one published case involving aripiprazole, and none for olanzapine, lurasidone, or brexpiprazole. In addition to the limited publication history on SGA–MAOI treatment, clinicians may also be deterred by uncertainty regarding SGA mechanisms and the risk of serotonin syndrome or other adverse outcomes. This paper describes the case of a 54-year-old male with a history of psychotic unipolar depression treated with a combination of phenelzine, aripiprazole, and quetiapine, and reviews the 12 published cases of SGA–MAOI combination therapy with a focus on the pharmacological basis for serotonin syndrome, and the SGA mechanisms that should not be associated with a risk for this syndrome.