The objective of this study was to fabricate and assess the structure and mechanical performance of PLA reinforced by aligned discontinuous alkali treated natural fibre mats. The novel aspect of this work was in terms of composite processing, in particular, the use of fibre mats produced using a dynamic sheet former (DSF) wherein discontinuous treated fibres were aligned. Composites with different fibre weight contents were assessed using optical microscopy, scanning electron microscopy (SEM) and tensile testing. It was found that the fibres had a reasonable degree of alignment parallel to the DSF rotation direction together with good fibre dispersion. Tensile strengths of harakeke and hemp composites up to 101.6 MPa and to 87.3 MPa were achieved, approximately 90 and 60% higher respectively than PLA (53.9 MPa). It was also found that minimum and critical fibre volume fractions for harakeke and hemp fibre composites were lower than that found for injection moulded composites, due to better reinforcement efficiency obtained as a result of increased fibre alignment.