Trichoderma spp. have been widely used as a biological control agent for plant disease including basal stem rot (BSR) in oil palm. Trichoderma spp. control pathogens through mycoparasitism, antibiosis and triggering induced systemic resistance (ISR) in plants during the colonisation of plant roots, limiting the manifestation of the pathogenic fungi. In this study, we investigated the role of endophytic Trichoderma virens as a plant-growth promoter and its ability to prime the immune system of the host through ISR in oil palm. Mixed application of two endophytic isolates of T. virens 7b and 159c was found to significantly enhance the growth and development of oil palm seedlings, in terms of height, girth and chlorophyll content compared to individual treatment. However, results showed that individual treatment of 7b and 159c was better in lignin biosynthesis. Plant defence-related enzyme activities; peroxidase, polyphenol oxidase, superoxide dismutase and phenylalanine lyase were prominently elevated in the leaves of oil palm seedlings upon treatment of the respective T. virens isolates via plant roots. This study demonstrated the triggering of ISR in oil palm seedlings via T. virens treatment and proving that the inoculation of T. virens isolates 7b and 159c were able to promote the vegetative growth and development of oil palm seedlings.