44-year-old Fadnavis, a third time MLA and the second Brahmin to occupy the top post in the state, was administered the oath of office and secrecy by Governor C Vidyasagar Rao at the Wankhede Stadium in the presence of Prime Minister Narendra Modi, BJP President Amit Shah, several Union ministers and veterans L K Advani and MM Joshi among others.
Top industrialists along with other eminent personalities, including from Bollywood, and Fadnavis' banker wife Amruta, were present at the packed venue when seven Cabinet Ministers and two Ministers of State also took oath.
Former ally Shiv Sena chief Uddhav Thackeray, whose party had decided to boycott the event citing "constant humiliation" by BJP ahead of government formation, attended the event along with his wife after a last-minute call by BJP President Amit Shah.
All eyes were on Modi and Uddhav, who shook hands and exchanged pleasantries.
With 121 BJP MLAs in a House of 288, Fadnavis is heading a minority government that has been asked to prove majority in two weeks. Sharad Pawar's NCP with 41 MLAs has already declared unconditional outside support to the new government.