This article contributes to the study of electoral volatility in two-round majority elections by examining the 2014 and 2020 municipal elections in Montpellier (France). Our article estimates electoral volatility using ecological inference from aggregated electoral and census data collected at the polling station level. First, this study underlines that vote shifts are mainly intra-bloc volatility. Moreover, our results also show that electoral volatility—particularly remobilization and intra-bloc volatility—is more frequent within polling stations with politically interested categories and young people. Furthermore, this study suggests that social context is an essential determinant of volatility.