The general purpose of this study was to explore the measurement of life satisfaction in older adolescents over time using a nationally representative sample. One specific aim was to capitalize on a pre-existing dataset that included a measure of life satisfaction yet to be validated. Another specific aim was to examine the measurement invariance of the best fitting model for this scale across gender, time, and the interaction of these two variables. Participants (N = 7643) completed a 12-item scale designed as part of the Longitudinal Surveys of Australian Youth (LSAY) project. Participants of the 2003 Cohort completed this scale across three waves. Single-group confirmatory factor analyses supported the superiority of a two-factor model (i.e., current life satisfaction; satisfaction with future prospects) of life satisfaction in the overall sample and across gender and time. Results from a series of multi-group confirmatory factor analyses indicated that the two-factor model exhibited strong measurement invariance (i.e., configural, metric, scalar, invariant factor co/variances and uniqueness) across gender, time, and gender × time. Collectively, these findings support the LSAY scale as a stable measure of perceived life satisfaction in older Australian adolescents.