Western New Guinea remains one of the last biologically underexplored regions of the world, and much remains to be learned regarding the diversity and evolutionary history of its fauna and flora. During a recent ornithological expedition to the Kumawa Mountains in West Papua, we encountered an undescribed species of Melanocharis berrypecker (Melanocharitidae) in cloud forest at an elevation of 1200 m asl. Its main characteristics are iridescent blue‐black upperparts, satin‐white underparts washed lemon yellow, and white outer edges to the external rectrices. Initially thought to represent a close relative of the Mid‐mountain Berrypecker Melanocharis longicauda based on elevation and plumage colour traits, a complete phylogenetic analysis of the genus based on full mitogenomes and genome‐wide nuclear data revealed that the new species, which we name Satin Berrypecker Melanocharis citreola sp. nov., is in fact sister to the phenotypically dissimilar Streaked Berrypecker Melanocharis striativentris. Phylogenetic relationships within the family Melanocharitidae, including all presently recognized genera (Toxorhamphus, Oedistoma, Rhamphocharis and Melanocharis), reveal that this family endemic to the island of New Guinea diversified during the main uplift of New Guinea in the Middle and Late Miocene (14.6 Mya), and represents an evolutionary radiation with high disparity in bill morphology and signalling traits across species. Rhamphocharis berrypeckers fall within the Melanocharis clade despite their larger beaks and should be included in the latter genus. Interspecific genetic distances in Melanocharis are pronounced (average interspecific distance: 8.8% in COI, 12.4% in ND2), suggesting a long history of independent evolution of all lineages corresponding to currently recognized species, including the Satin Berrypecker, which shares a most recent common ancestor with its sister species in the early Pleistocene (˜ 2.0 Mya).