West Sumatra province is one of the most earthquake-prone regions in Indonesia, with its capital city being Padang City. Buildings in Padang city should have the structural integrity of buildings, particularly for office buildings. However, many office buildings, such as the Lambung Bukit Subdistrict Office Building, were constructed without following the building standards. During the maintenance period, it was discovered that this Office Building, a two-story reinforced concrete structure, had lower than planned structural concrete quality (fc′ = 12.55 MPa, based on Hammer Test results) and exhibited damage and cracking. Therefore, a structural evaluation of the building’s strength should be done according to current Indonesian building codes. This study assesses the seismic performance of the office building through dynamic response analysis using the finite element program ETABS V21. The results indicated that column K1 (300 × 300) cannot withstand combined loads, particularly earthquake loads. A retrofitting of the building should be carried out so that the building can resist the working loads. The recommended retrofitting involves replacing existing walls with reinforced concrete (RC) shear walls. The re-analysis of the retrofitted building revealed a decrease in bending moment of 68.24% for the 1st-floor columns. This retrofit significantly increased the building’s structural capacity, meeting building code requirements and ensuring earthquake resistance and safety for office operations.