Background:A social mobilization (SM) initiative contributed to India’s success in polio elimination. This was the CORE Group Polio Project (CGPP), a partner of Uttar Pradesh (U.P.) SM Network and which continued its SM activities, even during the polio-free period through a network of multi-level social mobilizers. This paper assesses the effects of this community-level SM (CLSM) intervention on the extent of community engagement and performance of polio vaccination campaigns during the post-polio-endemic period (i.e., from March 2012 to September 2017). Methods:This study followed a quasi-experimental design. We used secondary, cluster-level data from CGPP India’s Management Information System, including 52 SIAs held from January 2008 to September 2017 in 56 blocks, covering 12 districts of U.P. We computed various indicators and performed Generalized Estimating Equations (GEE) based analysis to assess the statistical difference. We then estimated the effects of the SM intervention, using Interrupted time-series, Difference-in-Differences and Synthetic Control Methods. Also, estimated the population influenced by the intervention. Results:The performance of polio vaccination campaigns changed over time, with the intervention areas having better outcomes than non-intervention areas. The absence of community-level SM Net intervention during the post-polio-endemic period would have negatively impacted booth coverage, X-to-P conversion rate, Refusal-to-Acceptor conversion of intervention areas to 14.1 (range: 12.7 to 15.5), 6.3 (range: 5.2 to 7.3) and 7.4 percentage points, respectively. Community engagement would have reduced by 7.2 (range: 6.6 to 7.7) percentage points. The study guesstimated that the intervention averted at least 43 (range: 40 to 47) paralytic polio cases annually from the intervention areas, during the post-polio-endemic period. Conclusions:The absence of CLSM intervention would have significantly decreased the level of community engagement and negatively impacted the performance of polio SIAs of the post-polio-endemic period. The study provides evidence of an added-value of additional human resources dedicated to social mobilization to achieve desired vaccination outcomes in hard-to-reach or programmatically challenging areas.