ABSTRACT Conodonts and ostracods in the orogenic belt can provide valuable insights into the timing and effects of tectonic events. In this study, four species of conodonts and 24 species of ostracods are reported for the first time in the Hongliugou and Kalamaili Formations in the Harlik arc, southwestern Central Asian Orogenic Belt (SW CAOB). Among them, conodont species Caudicriodus woschmidti is the significant element in the lowermost Devonian conodont zone, indicating that the upper part of the Hongliugou Formation dates to the earliest Devonian (Lochkovian) age. The ostracod assemblages identified in the Hongliugou and Kalamaili Formations are characterised by the dominance of Palaeocopid and Metacopina elements, respectively, suggesting a change in environment from inner‐shelf to hemipelagic outer‐shelf. This transgression is associated with regional extension during the Early Devonian, likely subjected to the retreating subduction of the Paleo‐Asian Ocean. Furthermore, paleobiogeographic analysis of Devonian ostracods in the Harlik arc shows a prominent correlation with eastern North America and southern Europe. This suggests that the Harlik arc was probably located in the mid‐latitude region of the northern hemisphere, adjacent to the northeastern part of the Laurentia‐Siberia continent, during the Early to Middle Devonian.