The use of environmentally friendly approaches to improve crop productivity has gained considerable attention in sustainable vegetable production. This study was conducted during the summer of 2022 at the Horticulture Research Farm, The University of Agriculture, Peshawar, Pakistan, to evaluate the effects of Trichoderma harzianum and acetylsalicylic acid (ASA) on the growth and yield of chilli (Capsicum annuum L.) cv. P6. The experiment was arranged in a factorial Randomised Complete Block Design with three replications, comprising four levels of T. harzianum (0, 2, 4, and 6 kg ha-1) and four concentrations of ASA (0, 100, 200, and 300 mg L-1). The main effects of T. harzianum and ASA significantly improved plant growth, chlorophyll content, fruit characteristics, ascorbic acid content, and yield, while reducing the number of days to flowering and fruit set and disease incidence, compared with the untreated control. The highest levels of T. harzianum and ASA generally produced superior responses for most measured traits. However, the interaction between T. harzianum and ASA was generally not significant across all studied parameters. Overall, the individual application of T. harzianum and ASA demonstrated potential as environmentally friendly approaches for enhancing the growth, yield, and fruit quality of chilli under the agro-climatic conditions of Peshawar.