Recently, nanotechnology has emerged as a rapidly growing field focused on the fabrication, characterization, and application of nanomaterials. In the realm of wastewater treatment, nanomaterials play a crucial role in various processes, including adsorption, antimicrobial activity, photocatalysis, stabilization, water splitting, etc. Among these, photocatalysis is considered the most efficient and eco-friendly technique. Physical and chemical methods are widely employed for nanoparticle synthesis. However, they have drawbacks such as high labor requirements, high cost, and the use of extensive chemicals. In contrast, bio-based methods offer an eco-friendly and economical approach to producing photocatalytically active nanomaterials with improved properties. Bio-based methods utilize biological units, such as plant extracts, as sources of reducing and capping agents in a one-pot synthesis system. This study reviewed reported studies on the bio-based synthesis of photocatalyst nanomaterials for photocatalytic applications. Bio-based synthesis has been employed to create native and non-metal/metal-doped photocatalysts, heterojunctions, and nanocomposites using plant extracts. The primary bio-analysts present in these extracts include ascorbic acid, gallic acid, citric acid, phenolic compounds, flavonoids, and other chelating agents. These diverse bio-analysts produce superior photocatalysts compared to those synthesized using chemical methods. This review summarizes the stands of bio-based routes over chemical-based synthesis methods, highlighting improvements in bandgap, surface hydrophilicity, oxygen vacancies, and photocatalytic degradation efficiency. Additionally, it extensively covers nanomaterial synthesis methods, bio-based synthesized photocatalyst nanomaterials, and their photocatalytic applications. Conclusively, adopting bio-based synthesis routes not only improves the photocatalytic properties of photocatalysts but also reduces synthesis costs and minimizes the use of harmful chemicals.