Objective This study aimed to evaluate the impact of the Stand Up Victoria intervention - a multicomponent workplace intervention that successfully reduced workplace sitting - on productivity in the short- and longer-term. Methods Desk-based workers [5-39 per worksite; 68% women; mean age 45.6 (standard deviation 9.4) years] were cluster randomized by office worksite to receive intervention (7 worksites, 136 workers) or control (7 worksites, 95 workers). The intervention used organizational-, environmental-, and individual-level approaches to address workplace sitting. Productivity outcomes were measured via the Health and Work Questionnaire (HWQ; 10 outcomes) and Work Limitations Questionnaire (WLQ; 5 outcomes), administered at 0 (baseline), 3 (initial), and 12 (long-term) months. Intervention effects were assessed by linear mixed models, accounting for repeated measures and clustering, baseline values, and potential confounders. Evaluable case and multiple imputation analyses were used. Results At 12 months, trends for improvement were observed in the HWQ non-work satisfaction subscale (P=0.053) and stress item (P=0.086). Intervention effects on remaining outcomes for the HWQ were small and non-significant at both timepoints. At 3 months, intervention effects showed significant improvements in the WLQ mental demands subscale (P=0.043). At 12 months, intervention effects showed significant (P<0.05) small-to-moderate improvements in four WLQ outcomes (weighted total score, time-, mental-, and output demands), with physical demands showing a small significant worsening. Conclusions were robust to missing data assumptions. Conclusions The intervention improved some measures of productivity at 12 months, providing important evidence to the business case supporting workplace sitting-reduction interventions.