Governor H.R. Bhardwaj administered the oath of office and secrecy to Shettar at a simple ceremony in the glass house of Raj Bhavan in city centre.
Shettar, 56, took over from D.V. Sadananda Gowda, who was forced out of office without completing a year following months of dissidence orchestrated by the BJP's first chief minister in southern India, B.S. Yeddyurappa. Yeddyurappa was shown the door by the party last July over mining bribery charges.
Karnataka's new chief minister hails from a family with close association to the Rashtriya Swayamsevak Sangh (RSS) and the BJP's predecessor Jan Sangh.
Shettar is a four-time legislator representing Hubli rural constituency in Dharwad district, about 400 km north of Bangalore.