During 2018 season, we explored the virome of a declining 32-yr. old Blanc du Bois (Vitis spp.: ‘Florida D 6-148’ × ‘Cardinal’) vineyard in Texas. Total RNA extracts from 51 samples were pooled and subjected to Illumina high throughput sequencing (HTS). Analyses of the obtained ~23.5 million raw reads (76 nt each) revealed contigs specific to viruses and viroids, including 10 contigs (206 to 4,405 nt) with similarities to vitiviruses. RT-PCR tests of individual vines with two primer pairs designed from the HTS sequences revealed 11.8% (6/51) incidence of the Vitivirus. The complete ssRNA (+) genome of the virus, provisionally named as grapevine virus M (GVM), was determined via its RT-PCR amplification as two pieces of overlapping DNA fragments, and verification of its 5? and 3? extremities by RACE assays. The assembled Sanger-sequenced genome was 99.7% nt identical to the HTS-derived sequence. The complete genome of GVM is 7,387 nt, excluding the polyA tail and consists of five ORFs that are homologous and phylogenetically related to ORFs of grapevine-infecting vitiviruses. The replicase and coat protein genes of GVM were most identical to those of GVH at 66% nt & 75% aa and 79% nt & 89% aa levels, respectively. Based on current ICTV species demarcation criteria, GVM is proposed as a new species in the genus Vitivirus. The discovery of GVM is shedding more light on the evolution of vitiviruses across grapevine-producing regions of the world.