In analytical chemistry, derivatization is a widely used tool for targeted modification of analytes to improve detectability and chromatographic behavior, often enhancing the sensitivity and selectivity of analytical procedures. Minimizing the use of toxic organic solvents and reagents during sample preparation is of particular relevance. Deep eutectic solvents (DESs), which have proven effective as extractants in many applications and whose environmental profile depends on their composition, offer new possibilities by acting not only as solvents but also as alternative reaction media for derivatization. This review, for the first time, summarizes modern strategies for using such systems in chemical analysis for the derivatization of analytes. Three key approaches are considered: (i) sequential workflows (“extraction → derivatization” and “derivatization → extraction”), (ii) their simultaneous implementation within a single DES-based system, and (iii) the use of DES components as derivatizing reagents, which can reduce or eliminate the need for traditional toxic derivatization agents.