44-year-old Fadnavis was administered the oath of office and secrecy by Governor C Vidyasagar Rao in a grand function at Wankhede Stadium attended, among others, by Prime Minister Narendra Modi, several of his Cabinet colleagues, Chief Ministers of BJP-ruled states and those governed by allies.
Apart from Fadnavis, 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 during talks for formation of a coalition government, attended after a last minute call by party President Amit Shah, amid indications of a possible rapprochement between the two estranged Hindutva parties.
All eyes were on Modi and Uddhav, who shook hands and exchanged pleasantries.
Cabinet Ministers who were sworn in are Eknath Khadse, Sudhir Mungantiwar, Vinod Tawde, Pankaja Munde, all members of the BJP's state Core Committee, Prakash Mehta, Chandrakant Patil and Vishnu Savara. The Ministers of State are Dilip Kamble and Vidya Thakur.
Apart from BJP patriarch L K Advani, Union Ministers Nitin Gadkari, M Venkaiah Naidu, Ravishanker Prasad, Prakash Javadekar and Radhamohan Singh, Raman Singh, Manohar Parrikar, Anandiben Patel, Vasundhara Raje, BJP Chief Ministers of Chhattisgarh, Goa, Gujarat and Rajasthan respectively were present.
Among the allies, Punjab Chief Minister Parkash Singh Badal and N Chandrababu Naidu of Andhra Pradesh also attended the ceremony.
Fadnavis is only the second Brahmin Chief Minister after Shiv Sena's Manohar Joshi in the state dominated by Maratha politicians.
Fadnavis has become the 27th CM of Maharashtra and the 18th person to hold the post. He is the fourth politician from Vidarbha region to become CM.