In recent years, the problems of environmental pollution and energy scarcity have affected human life, and the green and low-carbon photocatalytic and electrocatalytic technologies have attracted widespread attention. Semiconductor-based photocatalytic and electrocatalytic technologies are very promising for ammonia synthesis applications. Since single semiconductors suffer from the disadvantages of low carrier separation efficiency and easy compounding, it is crucial to find co-catalysts that can enhance the performance of nitrogen fixation catalysts. Two-dimensional transition metal carbide/nitride/carbon nitride MXene, which have a promising application in photo- and electrocatalytic ammonia synthesis, are ideal for photo- and electrocatalytic nitrogen fixation owing to their good hydrophilicity, large specific surface area, excellent electrical conductivity and abundance of active sites for efficient catalysis of N₂ reduction. This paper mainly reviews the preparation of MXene and its composites and their progress in the field of photoelectrocatalytic ammonia synthesis. Firstly, the structural features of MXene and the preparation strategies of MXene and its complexes are briefly summarised. Secondly, the performance study of MXene-based composite catalysts for photo- and electrocatalytic ammonia synthesis is highlighted. Finally, the development direction of MXene-based composites is discussed and prospected.