A debris flow type of landslide is believed to have propagated from existing minor landslides and heavy rainfall on August 13, 2017, near the village of Kotropi (Mandi District, Himachal Pradesh), India. The disastrous landslide swept away two state transport buses causing 47 fatalities. A stretch of 300-m on National Highway-154 was completely buried under debris by a massive 1153 m of slope run-out extending over 190 m of slope width. The present research work aims at mitigation of Kotropi slope failure using helical soil nails. The preliminary study involves geotechnical and chemical testing of Kotropi soil. With favorable prevailing soil conditions, helical soil nails with length of 6 m and diameter 20 mm are used for stabilizing the failed slope. The stability of helical soil-nailed slope is determined by calculating factor of safety using limit equilibrium method which is also validated by numerical modeling using finite element subroutine PLAXIS 2D. A factor of safety of 1.54 is achieved by calculations in comparison with 1.67 from numerical modeling. Moreover, a decrease in maximum horizontal slope deformation is also achieved from 0.13 to 0.06 m.