Poly-lactic acid (PLA) has become a commonly used polymer for additive manufacturing because of its bio-derived nature, useful mechanical properties, and excellent processability. Reinforcing PLA with bio-derived materials has been shown to improve the physical, mechanical, and thermal properties of 3D printed composites and, in some cases, to produce active materials for shape-changing hygromorphic structures. PLA also displays shape memory as a response to changes in temperature, making it a popular choice for 4D printing. This review aims to present an overview of the current state of 3D/4D printing PLA composites with bio-derived reinforcements and highlight the recent progress and future opportunities. This comprehensive overview summarises the different forms of bio-derived reinforcements for PLA used in fused deposition modelling (FDM), factors influencing the resulting printed composites’ performance, and research gaps that need addressing. The current methods used before, during, and after printing to enhance the material properties and the impending need for innovative filament production and printing technologies have been brought to attention.