Barley (Hordeum vulgareL.) is one of the most produced cereal crops in the world. It has traditionally been used for the production of animal feed and for malting, as well as for human consumption. However, its production is highly affected by biotic stress factors, particularly the fungal pathogenBlumeria graminis(DC.) f. sp.hordei(Bgh), which causes powdery mildew (PM). In this study, a collection of 406 barley accessions from the USA, Kazakhstan, Europe, and Africa were assessed for resistance to PM over a 3-year period in southeastern Kazakhstan. The collection was grown in the field in 2020, 2021, and 2022 and was genotyped using the 9K SNP Illumina chip. A genome-wide association study (GWAS) was conducted to identify the quantitative trait loci (QTLs) associated with PM resistance. As a result, seven QTLs for PM resistance were detected on chromosomes 4H, 5H, and 7H (FDRp-values < 0.05). Genetic positions of two QTLs were similar to those of PM resistance QTLs previously reported in the scientific literature, suggesting that the five remaining QTLs are novel putative genetic factors for the studied trait. Haplotype analysis for seven QTLs revealed three haplotypes which were associated with total PM resistance and one haplotype associated with the high PM severity in the barley collection. Identified QTLs and haplotypes associated with the PM resistance of barley may be used for further analysis, trait pyramiding, and marker-assisted selection.