Background Non-pharmaceutical interventions (NPIs) were implemented by many countries to reduce the transmission of SARS-CoV-2, the causal agent of COVID-19. A resurgence in COVID-19 cases has been reported in some countries that lifted some of these NPIs. We aimed to understand the association between introducing/lifting NPIs and the level of transmission of SARS-CoV-2 as measured by the time-varying reproduction number (R) from a broad perspective across 131 countries. Methods We linked data on daily country-level estimates of R from the London School of Hygiene and Tropical Medicine (LSHTM) with data on country-specific policies on NPIs from the Oxford COVID-19 Government Response Tracker (OxCGRT), available between 31-December-2019 and 20-Jul-2020. We defined a phase as a time period when all NPIs remained the same and we divided the timeline of each country into individual phases based on the status of NPIs. We calculated the R ratio as the ratio between daily R of each phase and the R from the last day of its previous phase (i.e. before the NPI status changed) as a measure of the association between NPI(s) status and transmission of SARS-CoV-2. We then modelled the R ratio using a log-linear regression with introduction and relaxation of each NPI as independent variables for each day of the first 28 days following the change in the corresponding NPI. Findings A total of 790 phases from 131 countries were included in the analysis. Individual NPIs, including school closure, workplace closure, public events ban, requirements to stay at home, and internal movement limits, were associated with a reduction in R of 7–24% on Day 28 following the introduction although the reduction was only statistically significant for public events ban. Re-opening school, lifting ban on public events, lifting ban on social gathering of >10 persons, and lifting internal movement limits were associated with an increase in R of 11–25% on Day 28 following the relaxation, although the increase was only stastically significant for re-opening school and lifting ban on social gathering of >10 persons. The effects of introducing and lifting NPIs were not immediate; it took 8 days (interquartile range, IQR: 6–9) following the introduction to observe 60% of their maximum reduction in R and even longer (17 days, IQR: 14–20) following the relaxation to observe 60% of the maximum increase in R. In response to a possible resurgence of COVID-19, a control strategy of banning public events and social gathering (of >10 persons) was estimated to reduce R, with an R ratio of 0·71 (95% CI: 0·55-0·93) on Day 28; and with an R ratio of 0·62 (95% CI: 0·47-0·82) on Day 28 if measures to close workplaces is added. Interpretation Individual NPIs, including school closure, workplace closure, public events ban, ban on gathering size of >10 persons, requirements to stay at home, and internal movement limits, are associated with reduced transmission of SARS-CoV-2 but the effect of introducing/lifting these NPIs is delayed by 1–3 weeks, with this delay being longer when lifting NPIs. These findings provide additional evidence that can inform policy-maker decisions on the timing of introducing and lifting different NPIs, although it should be noted that R needs to be interpreted in the context of its known limitations.