Genetic mutations of CARD14 (encoding CARMA2) are observed in psoriasis patients. Here we showed that Card14^E138A/+ and Card14^ΔQ136/+ mice developed spontaneous psoriasis-like skin inflammation, which resulted from constitutively activated CARMA2 via self-aggregation leading to the enhanced activation of the IL-23-IL-17A cytokine axis. Card14^−/− mice displayed attenuated skin inflammation in the imiquimod-induced psoriasis model due to impaired IL-17A signaling in keratinocytes. CARMA2, mainly expressed in keratinocytes, associates with the ACT1-TRAF6 signaling complex and mediates IL-17A-induced NF-κB and MAPK signaling pathway activation, which leads to expression of pro-inflammatory factors. Thus, CARMA2 serves as a key mediator of IL-17A signaling and its constitutive activation in keratinocytes leads to the onset of psoriasis, which indicates an important role of NF-κB activation in keratinocytes in psoriatic initiation.