A bstract Yields of prompt and non-prompt J/ ψ , as well as $ \Upsilon $ (1S) mesons, are measured by the CMS experiment via their μ + μ − decays in PbPb and pp collisions at $ \sqrt {{{s_{\text{NN}}}}} = 2.76 $ TeV for quarkonium rapidity | y | < 2.4. Differential cross sections and nuclear modification factors are reported as functions of y and transverse momentum p T , as well as collision centrality. For prompt J/ ψ with relatively high p T (6.5 < p T < 30 GeV/ c ), a strong, centrality-dependent suppression is observed in PbPb collisions, compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. In the same kinematic range, a suppression of non-prompt J/ ψ , which is sensitive to the in-medium b-quark energy loss, is measured for the first time. Also the low- p T $ \Upsilon $ (1S) mesons are suppressed in PbPb collisions.