Chief Minister Pramod Sawant was administered oath of office and secrecy by Goa Governor P.S. Sreedharan Pillai on Monday.
Prime Minister Narendra Modi, Union Home Minister Amit Shah, BJP national president JP Nadda and a host of central BJP leaders were present at Dr Shyama Prasad Mukherjee stadium for the event.
More than 2,000 police personnel have been deployed at the venue.
The BJP has won 20 seats in the February 14 polls, just one short of a majority in the 40- member state Assembly. It also has support of five other MLAs — three independent and two from the Maharashtrawadi Gomantak Party.