This study aimed to investigate the sociodemographic and clinical correlates of a history of a suicide attempt in people with depression and their relationship with treatment outcomes and subsequent suicidal ideation and deliberate self-harm. Patients with depressive disorders according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, were recruited from 18 hospitals across South Korea. Data on sociodemographic and clinical characteristics were obtained, and scales assessing depression, anxiety, and general functioning were administered during the first 12 weeks of antidepressant treatment. Baseline characteristics, responses to treatment, and suicidal ideation/deliberate self-harm during the follow-up period were compared according to a reported history or not of a suicide attempt. In a total of 723 participants, 143 (19.8%) with a history of a suicide attempt had an earlier age of onset, longer duration of illness, and a greater number of depressive episodes. Levels of depression and anxiety were significantly higher at baseline in this group who also experienced significantly lower remission and response rates, as well as longer time to remission. The case group was more likely to experience new suicidal ideation and carry out a deliberate self-harm act during the 12-week treatment period. In conclusion, a history of a suicide attempt in a Korean population with depression was characterized by more severe psychopathology, poorer treatment outcomes, and higher subsequent suicidal ideation and self-harm. Therefore, more intensive and longer-term treatment with particular ongoing clinical attention to risk is indicated in patients with these distinct, chronic, and severe forms of depression and ongoing high suicide risk.