The world species of Piogaster Perkins are revised including the description of a new species: Piogaster variegata Bass, Bennett & Schwarzfeld, sp. nov. from Alberta, Canada. The new species is described and the seven previously known species are redescribed, with an illustrated key to all eight world species. Species relationships are examined using molecular data, including DNA barcodes and ultra-conserved elements (UCEs). Piogaster pilosator caucasica Kasparyan, syn. nov. is newly synonymized under Piogaster pilosator (Aubert). Piogaster pilosator is newly recorded from Germany and Norway and a lectotype is hereby designated. Piogaster albina Perkins is newly recorded from Hungary and Sweden. We also include new generic records of Piogaster from Italy and new generic provincial records from British Columbia and Alberta, Canada. We report a new host genus for Piogaster, bringing the total host count to three genera of Salticidae. For the first time, a male Piogaster specimen is unequivocally associated with a female in P. daisetsuzana Kusigemati. Associating European and North American males with females based on morphology alone remains problematic.