The B_c⁺ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the B_c⁺ meson in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of √s_NN = 5.02  TeV, via the B_c⁺ → (J/ψ → μ⁺μ⁻)μ⁺ν_μ decay. The B_c⁺ nuclear modification factor, derived from the Pb-Pb–to–pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the Pb-Pb collision centrality. The B_c⁺ meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.