Overexpressing Tau counteracts apoptosis and increases dephosphorylated β‐catenin levels, but the underlying mechanisms are elusive. Here, we show that Tau can directly and robustly acetylate β‐catenin at K49 in a concentration‐, time‐, and pH‐dependent manner. β‐catenin K49 acetylation inhibits its phosphorylation and its ubiquitination‐associated proteolysis, thus increasing β‐catenin protein levels. K49 acetylation further promotes nuclear translocation and the transcriptional activity of β‐catenin, and increases the expression of survival‐promoting genes (bcl2 and survivin), counteracting apoptosis. Mutation of Tau's acetyltransferase domain or co‐expressing non‐acetylatable β‐catenin‐K49R prevents increased β‐catenin signaling and abolishes the anti‐apoptotic function of Tau. Our data reveal that Tau preserves β‐catenin by acetylating K49, and upregulated β‐catenin/survival signaling in turn mediates the anti‐apoptotic effect of Tau.