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We describe and experimentally implement a single-ion local thermometry technique with absolute sensitivity adaptable to all laser-cooled atomic ion species. The technique is based on the velocity-dependent spectral shape of a quasi-dark resonance tailored in a J → J transition such that the two driving fields can be derived from the same laser source leading to a negligible relative phase shift. We validated the method and tested its performances in an experiment on a single 88 Sr + ion cooled in a surface radio-frequency trap. We first applied the technique to characterise the heating-rate of the surface trap. We then measured the stationary temperature of the ion as a function of cooling laser detuning in the Doppler regime. The results agree with theoretical calculations, with an absolute error smaller than 100 µK at 500 µK, in a temperature range between 0.5 and 3 mK and in the absence of adjustable parameters. This simple-to-implement and reliable method opens the way to fast absolute measurements of single-ion temperatures in future experiments dealing with heat transport in ion chains or thermodynamics at the single-ion level.PACS numbers: 37.10.Rs, 32.70.Jz, 37.10.Vz Laser cooled trapped ions offer the opportunity for a precise quantum control at the single particle level [1] that triggered the development of ion-based platforms dedicated to quantum information processing [2,3]. Cold ion based systems have also been proposed and applied for testing thermodynamics in the quantum regime [4,5] and quantum heat transport in network chains [6][7][8][9]. The latter applications need the development of thermometry techniques that should characterise in a short time the velocity distribution of a single-ion that possibly interacts with other ions in its direct environment. Since the first demonstrations of laser cooling of trapped ions [10,11], experimental thermometry tools have been developed together with theoretical models predicting stationary temperatures, for instance in the case of Doppler cooling [12,13]. Among the thermometry techniques for trapped ions we can distinguish between three large families.