Background Physical inactivity is rising globally, exacerbating the burden of preventable deaths and diseases. Despite extensive research on promoting physical activity in the workplace, synthesising the existing literature is challenging due to the wide variety of interventions and outcomes. This study aims to provide a comprehensive synthesis of intervention effects to inform health promotion initiatives and guide future research efforts. Methods In this umbrella review, we conducted systematic searches of six databases (Cochrane, MEDLINE, Embase, CINAHL, Scopus, and Web of Science) for systematic reviews and meta-analyses published between Jan 1, 2000, and May 31, 2024, evaluating workplace interventions targeting sedentary behaviour or physical activity in working adults aged 18 years and older without specific health conditions or mobility impairments. Outcomes encompassed any behavioural changes related to sedentary behaviour or physical activity. Evidence for each relevant combination of intervention and outcome categories was summarised using either meta-analysis or narrative synthesis, with primary study data extracted as needed. This study is registered with PROSPERO, CRD42020171774. Findings We included 36 systematic reviews and meta-analyses covering 214 unique primary studies. Despite considerable heterogeneity in the evidence, several effect trends emerged with moderate-to-high confidence. First, sit-to-stand workstations produced the largest reductions in sedentary time, decreasing it by up to 75 min per day (95% CI-109 to-41) when used alone, with reductions increasing by up to 33% when paired with psychosocial strategies. However, these interventions did not significantly increase physical activity at any intensity. Second, self-monitoring combined with psychosocial strategies yielded the largest increases in step count, with average gains of 1056 steps per day (371 to 1740). Third, no specific strategy consistently increased moderate-to-vigorous physical activity, although the available evidence remains sparse. Additional trends were observed but with lower confidence levels. Analysis of publication bias suggested an inflated effect of environmental-level interventions on occupational sedentary time. Adjusting for this bias using the trim-and-fill method only slightly reduced the effect size, but this result should be interpreted with caution due to high heterogeneity (I-2=84<middle dot>80%). Interpretation Current evidence highlights the modest effect of existing workplace interventions on physical activity. Some strategies, such as sit-to-stand workstations and gamified interventions, effectively reduce sedentary behaviour and encourage lighter forms of physical activity, but none consistently improves moderate-to-vigorous physical activity, which provides the greatest health benefits. With many countries falling short of the WHO target to reduce physical inactivity prevalence by 15% from 2010 levels by 2030, intensified efforts are needed to address this gap, meet global goals, and alleviate the health burden of physical inactivity. Funding None. Copyright (c) 2025 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license.