This study was established to assess the effects of IRF5 rs10488631 and CD28 rs1980422 single-nucleotide polymorphisms (SNPs) and HLA-DRB1 shared epitope (SE) allele on the prognosis and disease activity of rheumatoid arthritis (RA) patients. A total of 150 RA patients and 150 healthy controls were genotyped for the selected SNPs by real-time PCR. HLA-DRB1 SE was determined using LAB Type SSO Class II DRB1 typing. Our results suggest that HLA-DRB1, CD28, and IRF5 significantly discriminated (p < 0.001) RA patients and healthy controls (OR of single HLA-DRB1 SE allele = 2.431, CI = 1.467–4.027, OR of two SE alleles = 11.152, CI = 2.479–50.159), (OR of CD28 risk allele C = 2.794, 95% CI = 1.973–3.956) and (OR of IRF5 risk allele C = 4.925, CI = 3.26–7.439). Rheumatoid factor (RF) seropositivity was associated with HLA-DRB1 SE (p < 0.001) and IRF5 risk allele (p < 0.001). ACPA was significantly associated only with IRF5 risk allele (p < 0.001). A better response to methotrexate therapy was found in HLA-DRB1 SE non-carriers, and CD28 TT patients. This study demonstrated associations of HLA-DRB1 SE, CD28, and IRF5 with the risk of RA. HLA-DRB1 SE and CD28 rs1980422 can be used as predictors of methotrexate therapy response.