BACKGROUND:High levels of sitting are associated with increased risk of adverse health outcomes, including chronic disease. Extensive sitting at work is common, hence organisations should provide options to employees to reduce prolonged sitting. OBJECTIVE:To assess the efficacy and acceptability of a co-designed intervention to increase standing and reduce sitting in a public-sector office. METHODS:Forty-six adults participated in the quasi-experimental study (30 intervention; 16 control). The intervention involved providing sit-stand desks, prompts, workshops, and information emails to assist behavior change. Participants wore a thigh-mounted Actigraph GT3X+ for five working days and responded to an online questionnaire at baseline (BL), 6 (T1) and 13 weeks (T2) post intervention. RESULTS:Inclinometer-measured proportion of time standing increased in the intervention group from 14% (baseline) to 28% (T1) and 27% (T2) (67 minutes more standing over an 8-hour workday). Intervention participants reduced sitting time from 79% (BL) to 63% (T1 and T2), (80 minutes less sitting over an 8-hour workday). The control group showed no changes. The program was highly recommended (94%), and perceived to support behavior change (81%). CONCLUSIONS:This Move More, Sit Less intervention appears to be efficacious and acceptable. Future interventions should be co-designed to ensure culturally appropriate components and higher acceptability.