This randomised controlled trial examines the effectiveness of Cognitive-Behavioural Therapy for Suicide Prevention (CT-SP) in Dutch specialised mental health care. The study compares CT-SP plus treatment as usual (TAU) versus TAU alone among adult patients experiencing suicidal ideation or behaviour, regardless of their primary diagnosis. This intervention consists of 10 face-to-face CT-SP sessions delivered by trained psychologists across various specialised units at GGZ inGeest (depression/anxiety, bipolar disorder, personality disorders, etc.). The primary outcome measures reduction in suicide ideation severity and intensity using the Columbia-Suicide Severity Rating Scale, with assessments at baseline, 6 weeks, 12 weeks, and 9 months. This research builds on evidence showing that interventions directly targeting suicidality are more effective than those addressing it indirectly through treatment of underlying conditions like depression.