Domestic Cat Felis silvestris catus populations have been increasing since the 1970s in Western Europe. This increase is particularly notable in human habitats, such as gardens and parks, where Cats have locally become the most abundant carnivore. In urban contexts, understanding Cat behaviour could be important for biodiversity management. In this study, we analysed Cat predation on garden birds, using existing data from ringing programmes in France and Belgium. These types of data permit us to (1) investigate the bird species killed by Cats, (2) analyse changes in the proportion of birds killed by Cats over the years 2000–2015, and (3) compare the causes of bird mortality as reported by observers. The most affected species were passerines, both granivorous and insectivorous (Europian Robin Erithacus rubecula, Dunnock Prunella modularis, Greenfinch Carduelis chloris), who can frequently be found feeding on the ground or visiting feeders in the winter. Perched birds (Chiffchaff Phylloscopus collybita, Blackcap Sylvia atricapilla) were less represented. Ground-dwelling habits were significantly correlated to predation rates. Between 2000 and 2015, Cat-related mortality in garden birds increased by at least 50%, depending on the ringing programme studied, which coincided with an increase in Cat populations. Cat-related mortality is one of the leading causes of death reported by observers (12.8–26.3% of total dead birds) and occurs at the same order of magnitude as deaths due to collisions with windows. These results underline the need to consider Cats and their potential impacts on urban biodiversity management at garden and urban levels.