Soil is the major sink for a broad range of potentially toxic hydrophobic organic contaminants (HOCs), including polycyclic aromatic hydrocarbons (PAHs). PAHs are widely distributed affecting the physicochemical and biological properties of soil. These HOCs have significant human and environmental health concerns. The application of mineral-based conventional fertilisation and other chemical treatment methods to stimulate microbial catabolic activities is however costly as well deleterious to soil quality and health. Soil amendment with organic waste materials with a particular interest in the lignocellulosic ones for the remediation of contaminated soil has become a good substrate option for microbial growth and improvement of soil quality due to their lower cost, eco-friendly, sustainable, feasible and practical nature in the environment. Therefore, this thesis aimed to investigate the impact of various organic materials as sources of nutrients and microbial inocula for enhanced PAHs biodegradation in contaminated soils. The study comprised of three sets: the effects of application ratios of different organic materials (spent brewery grains, spent mushroom compost and biochars); fungal treatment and immobilisation study of organic material (in particular brewery spent grains) and nitrogen amendments on the biodegradation of 14C-phenanthrene. Results revealed that the biodegradation of phenanthrene was improved in soils after the addition of organic waste materials. In addition, the results showed that microbial catabolism and biodegradation of phenanthrene can be facilitated by the addition of smaller amounts of organic waste materials into the soil. Furthermore, improving the efficiency of organic waste material by pre-treatment and immobilisation methods using white-rot fungi were observed to promote higher catabolic response as well as influence the physicochemical properties and biological activity of amended soils. This thesis provides insights and evidence supporting the values of organic materials as nutrient supplements; appropriate ratios for soil amendment, and fungal immobilisation and fungal pre-treatment of waste materials as key mechanisms to stimulate and promote the bioactivities and biodegradation of PAHs in contaminated soil.