There remains a need to identify effective smoking cessation interventions in severely disadvantaged populations. This trial aimed to examine the effectiveness of an intervention (Call it Quits) developed to promote smoking cessation and delivered by community social service case-workers. Call it Quits was a pragmatic, parallel randomised trial of a case-worker delivered smoking cessation intervention conducted in a non-government community social service organisation in New South Wales (NSW), Australia. Adult smokers requiring financial assistance were randomly assigned to the five-session Call it Quits intervention or usual care control group. Of the 618 eligible individuals, 300 were randomised to the intervention group, of whom 187 (62%) consented and 318 were randomised to the control group, of whom 244 (77%) consented, resulting in 431 participants. The primary outcome measure was self-reported continuous abstinence up to 6-month follow-up with biochemical verification. Primary analysis was performed using all the available data from participants under the assumption the data is missing completely at random, followed by sensitivity analyses. No statistically significant differences in the primary outcome were found (1.4% in the control group versus 1.0% in the intervention group, OR = 0.77, p = 0.828). A multi-component smoking cessation intervention delivering motivational interviewing-based counselling and free NRT by a trained case-worker within a community social service setting was not effective at achieving abstinence in a highly disadvantaged sample of smokers but increased attempts to stop and led to a reduction in number of cigarettes smoked daily. •First smoking cessation trial in a community based social service setting•Participants were socioeconomically disadvantaged smokers with comorbidity•Case-worker delivered intervention were not effective at aiding abstinence•Important gains were made in reductions in cigarettes smoked and quit attempts.