Significant developments are observed in the design of composite building materials nowadays, especially on environmental and sustainability issues. For structural usage, nowadays researchers reveal lime, which is the traditional binding material known since ancient times. Lime known for its sustainable feature is often used with supplementary cementitious materials (SCM) such as metakaolin, fly ash, ground granulated blast furnace slag, and silica fume due to unfavourable properties regarding durability, strength, and slow hydration rate. On the other hand, cellulosic fibres with the advantages such as low density, high tensile strength, and moderate elastic modulus have cost competitiveness and eco-efficiency for fibre-reinforced composites. The structural use of cellulosic fibres may be possible if the degradation of hemp fibres in an alkali environment is mitigated. In this study, the experimental studies on hemp fibres were carried out by comparing with two types of macro synthetic fibres in a lime+metakaolin (L+MK)-based matrix. Durability as well as compressive and flexural characteristics were addressed in those fibrous matrices. First time in the current literature, macro synthetic fibres were included in the lime-based mixture. Besides, as a new contribution, coarse lightweight aggregates (LWA) were incorporated into this type of matrix with those fibres. The experimental findings indicate that the degradation of hemp fibres can be mitigated successfully, and three types of fibrous mixtures provide proper mechanical characteristics in their categories.