Background: From a network perspective, temporal stability of network structures over the course of psychotherapy may give more insights into underlying mechanisms and thus provide the benefit of guiding researchers and clinicians towards more complex and dynamic thinking about mental disorders and its risk factors. For that reason, this study used network analysis to examine changes in interrelations of depressive symptoms and suicidal ideation in patients undergoing cognitive behavioural therapy treatment (CBT). Method: Outpatients with depressive symptoms (N = 401) were assessed with the Beck Depression Inventory three times (pre-CBT, after 12 sessions, and post-CBT) during CBT. Gaussian graphical models were used to estimate the relationships among symptoms. Measures of connectivity, community structure, centrality, and predictability were used to compare networks before, during, and after CBT. Results: The severity of depressive symptoms and suicidal ideation significantly decreased over the course of therapy, but connectivity in the networks significantly increased. Communities of symptoms changed during treatment: before CBT bodily, cognitive, and affective symptoms clustered together; one more cluster emerged after 12 sessions of CBT (changes in sleeping and eating patterns); (mostly) affective–bodily and (mostly) cognitive clusters were observed after CBT. The most central and predictable symptom was worthlessness at baseline and after 12 sessions, and loss of energy and self-dislike at post-treatment. Suicidal ideation was one of the least central symptoms in the three networks of depressive symptoms. Discussion: Rather surprising from a network perspective, network connectivity increased during CBT with decreasing severity of depressive symptoms (and suicidal ideation). Furthermore, the associations among symptoms and their centrality changed during the course of therapy. Implications for clinical practice as well as the impact of ideosynctratic associations of symptoms and risk factors will be discussed.