An unstructured Extended Finite Element-based Digital Image Correlation (X-DIC) method is proposed for analysing displacement fields of a rock specimen having a discrete discontinuity. The principle of the X-DIC method is described in the paper and is validated by laboratory experiments. In the experimental setup, a cylindrical hole and an artificial discontinuity plane are embodied into a cuboidal rock specimen and tested under uniaxial compressive load. The surface of the specimen is speckled, and its images taken during the loading process are analysed using the X-DIC algorithm. The results show that the X-DIC can capture non-linear displacement fields and displacement jumps across the discontinuity plane and is effective in estimating the stiffness of joints. The method can also indicate the rock specimen’s onset of cracks and failure before it is visible to the naked eye. It is also demonstrated that X-DIC is a robust method for capturing full-field displacements, in a non-contact manner and can be applied in various rock engineering applications.