Winter wheat is an important cereal crop grown in the Southern Great Plains of the United States. In this region, it is often planted for dual-purpose use as such early seedling vigor and regrowth ability after grazing are important for both forage and grain production. The objective of this study is to map quantitative trait loci (QTLs) and identify single nucleotide polymorphisms (SNP) markers associated with early seedling vigor and regrowth vigor that are crucial for cool-season forage production in winter wheat pasture. A genome-wide association mapping study (GWAS) was conducted using 200 diverse winter wheat lines from a hard winter wheat association mapping panel. The panel was genotyped with the wheat iSelect 90K SNP array. Phenotyping of the traits was done under controlled greenhouse conditions in a randomized complete block design with six replications in total from two repeated experiments. For early-seedling vigor evaluation, data were collected 45 days after planting on shoot length, number of shoots, and dry biomass of clipped forage samples. The same traits were collected again from regrowth two weeks after clipping for regrowth vigor evaluation. Significant differences for all traits studied were observed among lines. Using general linear model (GLM) and mixed linear model (MLM), multiple significant QTLs of the traits evaluated were detected on different chromosomes. The findings in this study enable us better understanding genomic regions controlling seedling biomass performance of winter wheat. Once validated, the significant SNPs will be used in marker-assisted selection of early-seedling vigor and regrowth vigor traits during dual-purpose wheat breeding.