A laterally aligned flexible composite linear worm-based piezoelectric energy harvester made up of piezoelectric barium titanate nanoparticles and a three dimensional gel network of calcium alginate biopolymer was aimed to harness the low frequency mechanical energy. It is highly desirable to fabricate innovative micro/nanostructures for high performance energy harvesting beyond the conventional thin films, and small scale fabrication of nanowires (or rods). The open circuit voltage of a single composite worm-based energy harvester (diameter ≈ 550 μm, length ≈ 2.5 cm) increases up to 5 times by increasing the frequency of mechanical load (11 N) from 3 to 20 Hz. Similarly, 1.5 times voltage increment was observed by increasing the length of the composite worm from 1.5 to 3.5 cm upon the bio-mechanical hand force. The energy harvester can function as an efficient portable/wearable self-powered device due to its good flexibility, and multiple lengths of composite linear worms can be utilized to drive low-power electronic devices. In this work, the composite worms were prepared by an ionotropic gelation approach, which is eco-friendly, non-toxic, having low processing temperature/time, and potential for cost-effective, large-scale fabrication, making it suitable for low frequency based self-powered devices.