INTRODUCTION: Smoking cessation support is increasingly delivered in primary care by auxiliary healthcare workers in place of healthcare professionals. However, it is unknown whether this shift might affect the quality and impact of the support delivered. METHODS: Data from the iQuit in Practice randomized control trial of cessation support in General Practice was used (N = 602). Analyses assessed whether cessation advisor type (nurse or healthcare assistant [HCA]) was associated with abstinence (primary outcome: self-reported 2-week point prevalence abstinence at 8 weeks follow-up), the advice delivered during the initial consultation, pharmacotherapies prescribed, patient satisfaction, initial consultation length, and the number and type of interim contacts. RESULTS: There were no statistically significant differences in abstinence for support delivered by HCAs versus nurses at 8 weeks (HCAs 42.8%, nurses 42.6%; unadjusted odds ratio [OR] = 1.01, 95% confidence interval [CI] = 0.73 to 1.40), or at 4 weeks or 6 months follow-up. There were no statistically significant differences in advice delivered, the types of pharmacotherapies prescribed or patient satisfaction. Compared with nurses, HCA consultations were longer on average (HCAs 23.6 minutes, nurses 20.8 minutes; P = .002) and they undertook more interim contacts (HCAs median 2, nurses median 1; P < .001), with contact more likely to be face-to-face than phone call (HCAs 91.2%, nurses 70.9%; OR = 4.23, 95% CI = 2.86 to 6.26). CONCLUSIONS: HCAs appear equally effective as nurses in supporting smoking cessation, although they do this with greater patient contact. Using auxiliary practitioners to deliver cessation support could free up nurse time and reduce costs. IMPLICATIONS: This study found that primary care patients receiving smoking cessation support from auxiliary healthcare workers were just as likely to be abstinent up to 6 months later as those patients seen by nurses. While the auxiliary healthcare workers achieved this with slightly increased patient contact time, the advice delivered, pharmacotherapies provided and patient satisfaction were similar to that of nurses. Expanding the auxiliary healthcare worker role to include smoking cessation support could increase role satisfaction and reduce the costs of cessation support delivery in primary care.