It is not known if there are discernible patterns in method lethality over successive episodes of self-harm and, if so, how these may be differentially associated with risks of self-harm repetition and suicide. Latent trajectory modelling estimated variation in patterns of suicide attempt lethality in 1,719 individuals attended by ambulance services on at least three occasions between 2012 and 2016. Cox regression modelling investigated hazards of suicide attempt repetition, all-cause, and suicide mortality as a function of these patterns. Two distinct trajectories provided optimal fit (BIC: -39,464.92). The first (Low/Moderate to Low/Moderate Lethality group; 92.5%) consisted of those consistently using methods associated with low to moderate potential lethality throughout the observation period. The second (High to Low/Moderate Lethality group; 7.5%) consisted of those who initially used methods with higher potential lethality but who switched to methods characterised by lower lethality. There were no significant differences between groups in the hazards of reattempting suicide (Hazard Ratio [HR] = 1.41, 95% CI 0.76 to 2.59) or all-cause mortality (HR = 1.21, 95% CI 0.63 to 2.32). However, those assigned to the High to Low/Moderate Lethality trajectory group may be at greater risk of suicide (Sub-Hazard Ratio [SHR] = 2.82, 95% CI 1.16 to 6.86). There may be discernible sub-groups of patients with important differences in clinical treatment needs and suicide risk profiles. These differences should be considered when undertaking psychosocial risk/needs assessments with those presenting to clinical services following self-harm.