Background and Objective: Within-visit blood pressure variability (BPV) is predictive of cardiovascular events independent of mean blood pressure (BP) levels and may serve as marker of cardiovascular aging. This study aimed to explore changes in BPV by age, and sex in May Measurement Month (MMM) 2019 survey participants. Methods: Adults (≥18 years) were surveyed opportunistically from 92 countries and up to three standardized seated BP readings were recorded. This analysis included all participants who were not taking BP-lowering medication and with complete data on age, sex, and three valid BP recordings. Three indices of BPV were compared: the standard deviation (SD), coefficient of variation (CV), and variation independent of the mean (VIM). A linear regression model was created for each index. Models were adjusted for mean BP, age, sex, and an interaction between age and sex. Age and mean BP were each included as natural cubic splines with 11 and 5 knots, respectively, to allow for flexibility with modelling relationships. Results: Data from 842,356 participants were included. The mean age was 42.9 (SD 15.9) years and 51.5% were female. Patterns of BPV from 18-90 years and by sex were consistent across BPV indices. Systolic BPV was higher in female than male participants between the ages of 30 and 80. In female participants, systolic BPV declined with age from 18-25, after which systolic BPV increased with age. In male participants, systolic BPV declined with age from 18-45, after which systolic BPV increased with age. Diastolic BPV was highest at the youngest and oldest ages, and lowest between 45 and 55 in both sexes. Conclusions: There was a highly consistent pattern amongst three commonly used indices of BPV in their relationships with age and sex. The BPV of screened adults was lower in males than females and varied non-linearly with age, with markedly higher BPV at younger and older ages, with distinct patterns of variation observed between systolic and diastolic BPV.