This study documents the introduction of the European Baltic prawn, Palaemon adspersus Rathke, 1837 to the coastal waters of northeastern North America, specifically the west coast of Newfoundland and the Magdalen Islands in the Gulf of St. Lawrence, Canada. Species identification was verified using morphological and genetic criteria. In September 2011, the first specimens of P. adspersus were collected in Gulf of St. Lawrence waters near Stephenville Crossing, Newfoundland, Canada. In 2012, additional P. adspersus specimens were collected in this area and at St. Andrew’s, located further south in western Newfoundland and in 2013 several egg-bearing females were collected further north in York Harbour. Accidental transport by ballast water of ships seems the likely vector for transport of Baltic prawn to the Gulf of St. Lawrence from Northern Europe or the Caspian Sea. It is possible that this shrimp has a wider presence in Atlantic Canadian waters but, due to its close resemblance to native shrimp species, it may have been previously misidentified, as occurred with specimens collected from the Magdalen Islands. We further expect that other species of the genus Palaemon, including P. elegans Rathke, 1837 from the Baltic Sea or northeastern United States, and P. macrodactylus Rathbun, 1902 from the northeastern United States, may invade the Gulf of St. Lawrence. We provide an illustrated key for the identification of these exotic Palaemon species and to differentiate them from native members of the subfamily Palaemoninae.