A novel soybean variety, designated XR31L13 is provided. Also provided are the seeds of soybean variety XR31L13, cells from soybean variety XR31L13, plants of soybean XR31L13, and plant parts of soybean variety XR31L13. Methods provided include producing a soybean plant by crossing soybean variety XR31L13 with another soybean plant, methods for introgressing a transgenic trait, a mutant trait, and/or a native trait into soybean variety XR31L13, methods for producing other soybean varieties or plant parts derived from soybean variety XR31L13, and methods of characterizing soybean variety XR31L13. Soybean seed, cells, plants, germplasm, breeding lines, varieties, and plant parts produced by these methods and/or derived from soybean variety XR31L13 are further provided.