Abstract This study explores the development of fibre reinforced structural lightweight aggregate concrete (SLWAC) using sintered fly ash aggregate (SFA) as coarse aggregate. SFA is manufactured from fly ash, an industrial by-product, thus making SLWAC a sustainable building material. SLWAC of density 1800 kg/m3 is developed with and without the addition of synthetic polyolefin (macro and micro) fibres to achieve a target compressive strength of 40 MPa. The main objective of this study is to understand the mechanical properties of SLWAC made of SFA and the influence of fibres in improving mechanical properties of SLWAC. The effect of monofilament macro-synthetic fibre dosages of 0.2%, 0.4%, and 0.6%, as well as the fibrillated micro fibres of 0.02% on the mechanical properties of SLWAC is studied. Tests were carried out for understanding the stress-strain behaviour under compression, split tensile strength, and fracture behaviour under flexure. Digital image correlation technique is used to study the crack propagation in fracture and splitting tension tests. A significant improvement in flexural strength, splitting tensile strength and toughness of SLWAC is observed due to the addition of synthetic fibres. Fibres significantly contributed to load resistance by arresting both micro and macro cracks. Thus, with the help of synthetic fibres addition in SLWAC, the desirable mechanical properties for structural applications such as strength and ductility can be achieved at reduced density.