Governor Urmila Singh administered the oath of office to the septuagenarian, who has been chief minister for more than 16 years, at the historic Ridge here.
The 78-year-old took oath at 10.40 a.m. as the hill state's 13th chief minister in the presence of thousands of his supporters.
He first assumed office April 8, 1983, replacing Thakur Ram Lal.
Belonging to the erstwhile princely state of Rampur Bushahr, Virbhadra Singh entered politics at the age of 28.
