Shifts in species ranges are a global phenomenon, well known to occur in response to a changing climate. New species arriving in an area may become pest species, modify ecosystem structure, or represent challenges or opportunities for fisheries and recreation. Early detection of range shifts and prompt implementation of any appropriate management strategies is therefore crucial. This study investigates whether “first sightings” marine of species outside their normal ranges could provide an early warning of impending climate-driven range shifts. We examine the relationships between first sightings and marine regions defined by patterns of local climate velocities (calculated on a 50-year time scale). as lacking connections to warmer areas (climate ‘source’), where moving isotherms converge (‘corridors’), and places were isotherms locally disappear (‘sink’ areas), while also considering the distribution of observational effort (i.e. number of sampling days recorded for biological observations in global databases). Additionally, we investigate the latitudinal band first sightings were recorded in, and species’ thermal affiliations. We found that first sightings in climate sink and divergent regions occur independently of sampling effort and ocean area, indicating that climate velocity has influenced the distribution of first sightings in sink regions. The majority of our first sightings appear to be tropical and sub-tropical species moving towards high latitudes, as would be expected in climate warming. Our results indicate that first sightings are likely related to longer-term climatic processes, and could therefore have potential use to indicate likely climate-driven range shifts. The development of an approach to detect impending range shifts at an early stage will allow resource managers and researchers to better manage opportunities resulting from range-shifting species before they potentially colonise.