Background and Aims: Most homicide studies focus upon ‘acute’ situational intoxication as opposed to ‘chronic’ substance misuse. The aims of the study were to: (1) determine the extent of homicide offenders’ alcohol and drug use in the year preceding the homicide; (2) compare the individual characteristics of homicide offenders across levels of problematic substance use; and (3) compare homicide incident characteristics across levels of problematic substance use. Design and Setting: Observational study using data collected through face-to-face interviews in custodial and community correctional settings across Australia. Participants were recruited through an opt-in process. Participants: The data consist of 302 individuals convicted of murder or manslaughter. Measurements: We used the Alcohol Use Disorder Identification Test and Drug Abuse Screening Test to determine problematic alcohol or drug use. We also used a range of self-report measures to ascertain offender characteristics [socio-demographics, developmental experiences, criminal history, personality] and incident characteristics (who was killed, and situational intoxication). Findings: Of the sample, 38.8% displayed high levels of alcohol problems and 30.8% displayed high levels of drug problems. Those displaying high levels of alcohol and/or drug problems were more likely than those without high levels of alcohol and/or drug problems to report adverse developmental experiences, low education, financial difficulties, extensive criminal histories and high levels of trait anger, impulsivity and risk-seeking. In addition, offenders with problematic substance use were more likely to have killed non-family and to have used substances at the time of the homicide. Conclusions: High proportions of homicide offenders in Australia appear to have problematic substance use in the year preceding the homicide offence, and such use appears to be associated with a range of other challenging factors, including adverse childhoods, criminal involvement, low socio-economic factors and low self-regulation.