Plant Growth-Promoting Rhizobacteria (PGPR) have attracted much attention in agriculture biotechnology as biological inputs to sustain crop production. The present study describes a halotolerant phosphate solubilizing bacterium associated with quinoa plant roots. Based on a metabolic screening, one bacterial isolate, named QA2, was selected and screened for PGPR traits. This isolate solubilized both inorganic phosphate and zinc, produced indole-3-acetic acid, ammonia, hydrogen cyanide, cellulase, and (to be deleted) protease, and induced biofilm formation. We demonstrated that QA2 exhibited both antimicrobial and ion metabolism activities and tolerated high salt concentration at up to 11% NaCl. Genotyping analyses, using 16S rRNA and chaperonin cpn60 genes, revealed that QA2 belongs to the species of Bacillus velezensis. Using the quinoa model cultivated under a saline condition, we demonstrated that QA2 promoted plant growth and mitigated the saline irrigation effects. Analysis of harvested plants revealed that QA2 induced a significant increase of both leaf chlorophyll index by 120.86% (p < 0.05) and P uptake by 41.17% (p < 0.05), while the content of Na+ was drastically decreased. Lastly, a bibliometric data analysis highlighted the panoramic view of studies carried out so far on B. velezensis strains. Our investigation presents a holistic view of the potential application of B. velezensis as a biological inoculant to promote plant growth, control pathogen attacks, and mitigate the salinity effect of quinoa plants. Further investigations are still needed to demonstrate these effects in field conditions.