β-catenin signaling has recently been tied to the emergence of tolerogenic dendritic cells (DC). Here we demonstrate a novel role for β-catenin in directing DC subset development through IRF8 activation. We found that splenic DC precursors express β-catenin, and DC from mice with CD11c-specific constitutive β-catenin activation upregulated IRF8 through targeting of the Irf8 promoter, leading to in vivo expansion of IRF8-dependent CD8α+, plasmacytoid, and CD103+CD11b− DC. β-catenin-stabilized CD8α+ DC secreted elevated IL-12 upon in vitro microbial stimulation, and pharmacological β-catenin inhibition blocked this response in WT cells. Upon infections with Toxoplasma gondii and vaccinia virus, mice with stabilized DC β-catenin displayed abnormally high Th1 and CD8+ T lymphocyte responses, respectively. Collectively, these results reveal a novel and unexpected function for β-catenin in programming DC differentiation towards subsets that orchestrate proinflammatory immunity to infection.