Background The London Pathway Project (LPP) is an innovative whole‐systems approach to addressing the needs of offenders who have severe personality disorder, with the goal of reducing their risk of harm. Previous research has evaluated the initial implementation of the LPP. Aims This paper focused on evaluating the impact of the LPP on a number of criminogenic needs over time and its impact on the risk of reoffending and harm compared with a similar group who did not experience the pathway. Method Data for men who had been identified for the LPP were used to explore changes in key criminogenic needs an average of 11 months after commencing on the pathway. In addition, Offender Assessment System data was used to match men who had experienced the LPP for at least 12 months to a comparison group on key demographic and criminal history variables. Changes in validated risk assessment devices and changes in practitioners' perception of risk were examined. Results The LPP was associated with desirable within‐individual change for most of the criminogenic needs explored. However, strong non‐desirable changes in lifestyle and associates were also identified, but this was particularly the case for those sentenced to prison. When compared with a matched group, those identified for the pathway showed a significant reduction on an objective measure of risk of reoffending but were rated as having significantly increased risk of harm on the basis of practitioner's perceptions. There was no evidence that greater progression along the pathway was associated with greater benefits. Conclusions This is the first impact evaluation of the LPP, and the results were generally positive in terms of its relation to criminogenic needs and risks. Much more research that clearly links project inputs to actual behavioural outcomes, such as later reoffending, is needed. Implications This initial evaluation of the impact of the LPP could be used as baseline data to examine the impact of the pathway over time, and with greater precision (e.g. matching on personality features). Copyright © 2017 John Wiley & Sons, Ltd.