Summary Many plant‐pathogenic bacteria suppress pathogen‐associated molecular pattern ( PAMP )‐triggered immunity by injecting effector proteins into the host cytoplasm during infection through the type III secretion system ( TTSS ). This type III secretome plays an important role in bacterial pathogenicity in susceptible hosts. X anthomonas axonopodis pv. manihotis ( X am ), the causal agent of cassava bacterial blight, injects several effector proteins into the host cell, including TALE1 Xam . This protein is a member of the T ranscriptional A ctivator‐ L ike effector ( TALE ) protein family, formerly known as the AvrBs3 / PthA family. TALE1 Xam has 13.5 tandem repeats of 34 amino acids each, as well as two nuclear localization signals and an acidic activation domain at the C ‐terminus. In this work, we demonstrate the importance of TALE1 Xam in the pathogenicity of X am . We use versions of the gene that lack different domains in the protein in structure–function studies to show that the eukaryotic domains at the 3′ end are critical for pathogenicity. In addition, we demonstrate that, similar to the characterized TALE proteins from other X anthomonas species, TALE1 Xam acts as a transcriptional activator in plant cells. This is the first report of the identification of a TALE in X am , and contributes to our understanding of the pathogenicity mechanisms employed by this bacterium to colonize and cause disease in cassava.