In recent years, the second-highest mortality rate of any cancer worldwide has been breast cancer (BC), which is one of the three most common and deadly cancers among women. Detecting BC in its earliest stages facilitates treatment, reduces death risk, and improves survival rates for patients. Biosensors have garnered considerable attention in recent years for the early diagnosis of BC owing to their high sensitivity, simplicity, low cost, and low detection limit compared to other diagnostic technologies. Polymer nanocomposites (PNCs) containing conductive nanoparticles (NPs) have been used as electrochemical biosensors. In this study, we review recent developments in electrochemical biosensors based on PNCs containing metallic NPs and carbon nanomaterials (carbon nanotubes and graphene) for the diagnosis of biomarkers associated with BC. The key performance characteristics of electrochemical biosensors, such as linear detection range, limit of detection (LOD), and response time, along with the numerous BC biomarkers and various NPs for the fabrication of biosensors are discussed. Additionally, future challenges of electrochemical biosensors and hindrances to their use in clinical practice are explored.