Mutation or ablation of T cell factor 1 and lymphocyte enhancer factor 1 indicated involvement of the Wnt pathway in thymocyte development. The central effector of the Wnt pathway is β-catenin, which undergoes stabilization upon binding of Wnt ligands to frizzled receptors. We report here that conditional stabilization of β-catenin in immature thymocytes resulted in the generation of single positive T cells that lacked the αβ TCR and developed in the absence of pre-TCR signaling and TCR selection. Although active β-catenin induced differentiation in the absence of TCRs, its action was associated with reduced proliferation and survival when compared to developmental changes induced by the pre-TCR or the αβ TCR.