The marine red alga Laurencia brandenii collected from the southwest coast of India (Indian Ocean) was extracted and fractioned using column chromatography. The individual fractions were evaluated in vitro via antimicrobial activity against six species of Microbial Type Culture Collection and three species of clinical human pathogens, antipest activity on Sitophilus oryzae, maggoticidal activity against 2nd instar larvae of Sarcophaga sp. and termiticidal activity against Microtermes obesi. It was found that the fraction eluted using petroleum ether:chloroform (6:4) exhibited broader biological activities. The phyco-constituents of the active fraction were identified by gas chromatography-mass spectrometry (GC-MS) analysis. The GC-MS profile of the active fraction revealed that the main constituent was octadecadienoic acid (49.75%) followed by n-hexadecanoic acid (14.24%), which might have a functional role in the biological activities. The overall activity profile envisages that these bioactive compounds from L. brandenii could be utilized as a renewable natural resource for the development of novel environmental-compatible formulations for the control of human pathogens, pests, termites and maggots.