Over 60% of the landmass in India is prone to seismic hazards. However, the rapid transformation of rural areas into urban centres has led to a huge increase in the construction of multi-storey buildings. In India, the built environment in the past few decades comprises mid-rise structures constructed using reinforced concrete (RC). However, several such RC structures have irregular plans, which are known to be highly vulnerable under severe seismic loads. In the present study, a G + 10-storey L-shaped building with plan irregularities is analysed to investigate its seismic response. The response spectrum method and the nonlinear time history method are used to perform seismic assessment. The performance of the structure under the code prescribed loads is compared for the existing IS 1893(P1):2016 and the latest provisions of IS 1893:2023 (draft). The results from the analysis allow for an examination of critical structural response parameters, such as inter-storey drift, maximum displacement, and Storey shear. Based on the results obtained in the current investigation, it was observed that the building’s seismic response is highly influenced by plan irregularity. The results also indicate that the L-shaped building is highly unstable due to the dominance of torsional modes. Additionally, the results obtained from using a shear wall with and without boundary elements at optimal locations resulted in the reduction of structural response by 50% and 43%, respectively.