It is well known that politicized identities are especially good predictors of collective action, but very little is known about what these identities are. We propose that moral identity content plays a central role in politicized identities. We examined this among (un)politicized Americans in the 2012 US Presidential Elections. In a longitudinal community sample of US citizens (N = 760), we tracked personal (i.e., unique) and politicized (i.e., party activist) identity content: before, during, and after the election. We compared identity content of individuals who self-labelled as politicized (i.e., active party promoters) or unpoliticized (i.e., passive party supporters): (1) Democrats (n = 69) longitudinally and (2) Republicans (n = 69) cross-sectionally to examine three hypotheses: Moral identity content (e.g., trustworthy) would be more prominent in politicized (vs. unpoliticized) identities (H1); moral identity content overlapping politicized and personal identities predict seeing the self as politicized (H2) and engaging in party activism (H3). Results largely supported H1 and H2, but only weakly supported H3. We conclude that politicized identities are moralized identities that have a self-evaluative, but not strongly action-motivation, function. We discuss the implications of our findings and method for politicization research.