Inherited and <em>de novo</em> mutations in the <em>CARD14</em> gene promote the development of psoriasis, an inflammatory disease of the skin. CARD14 is a member of the CARMA protein family that includes the structurally related CARD11 adaptor that mediates NF-κB activation by antigen receptors. We investigated the mechanism by which <em>CARD14 </em>mutation in psoriasis activates NF-κB. In contrast to wild type CARD14, CARD14E138A and CARD14G117S psoriasis mutants interacted constitutively with BCL10 and MALT1, and triggered BCL10 and MALT1 dependent activation of NF-κB in keratinocytes. These alterations disrupted the inhibitory effect of the CARD14 linker region on NF-κB activation by facilitating BCL10 binding. Therefore, psoriasis mutations activated CARD14 by a mechanism analogous to oncogenic CARD11 mutations in non-Hodgkin B cell lymphomas. CARD14E138A also stimulated MALT1 paracaspase activity and activated both ERK1/2 and p38α MAP kinases. Inhibition of MALT1 with mepazine reduced CARD14E138A-induced expression of specific psoriasis-associated transcripts in keratinocytes. Our results establish the mechanism whereby gain-of-function CARD14 variants, which induce psoriatic disease in affected individuals, activate pro-inflammatory signaling.