o-Dianisidine dihydrochloride is primarily used as a reagent in chemical laboratories for the detection and quantification of various substances. It is commonly employed in colorimetric assays to measure peroxidase activity, particularly in biochemical and clinical research. The compound acts as a chromogen, producing a colored product when oxidized, which allows for easy visual or spectrophotometric analysis.

In industrial applications, it serves as an intermediate in the synthesis of dyes and pigments, contributing to the production of vibrant and stable colors in textiles, inks, and other materials. Additionally, it is utilized in the manufacturing of certain polymers and resins, where it plays a role in cross-linking processes to enhance material properties.

Due to its sensitivity to oxidation, it is also used in analytical chemistry for the detection of oxidizing agents, such as hydrogen peroxide, in various samples. However, its use is often limited due to its potential toxicity and carcinogenic properties, requiring careful handling and adherence to safety protocols.