Mental health counselling and support over the telephone or internet is increasingly common. Evaluating effectiveness requires outcome measures and understanding factors driving behaviour. This article describes a theory-driven evaluation of the one-month outcomes of a short-term solution-focused support session for anxiety or depression with a counsellor. The primary aim of the evaluation was to measure the outcomes of this session on service users’ help-seeking behaviour. It also sought to understand reasons for behaviour based on behaviour change theory. A secondary aim was to measure changes in feelings of stress and coping before and after the session, and collect evidence of the value of the service in terms of ‘consumer-defined recovery’. The evaluation found the service was effective, with the overwhelming majority taking some action, being more engaged with a health professional, having reduced feelings of distress, increased confidence to cope and less hopelessness. Improvements for service users included ‘reality testing’ the advice given and building commitment or intent to follow the advice, and ‘rehearsing’ so service users can demonstrate to themselves they have the skills required and can overcome any obstacles to following the advice.