Aims: During the last ~50 years, the population of black hole candidates in X-ray binaries has increased considerably, with 59 Galactic objects being detected in transient low-mass X-ray binaries, as well as a few in persistent systems (including ~5 extragalactic binaries). Methods: We collect near-infrared, optical, and X-ray information spread over hundreds of references to study the population of black holes in X-ray transients as a whole. Results: We present the most updated catalogue of black hole transients. This contains X-ray, optical, and near-infrared observations, together with their astrometric and dynamical properties. The catalogue provides new and useful information in both statistical and observational parameters and provides a thorough and complete overview of the black hole population in the Milky Way. Analysing the distances and spatial distribution of the observed systems, we estimate a total population of ~1300 Galactic black hole transients. This means that we have only discovered less than ~5% of the total Galactic distribution. The complete version of this catalogue will be continuously updated at http://www.astro.puc.cl/BlackCAT and in the Virtual Observatory, including finding charts and data in other wavelengths.Tables A.1 to A.4 are also available in electronic form at the CDS via anonymous ftp to (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A61