Prime Minister Narendra Modi was also there to attend the swearing-in ceremony.
The elevation of Adityanath, who has chequered rapport with the BJP leadership, has left many puzzled, with political circles abuzz with talk of the RSS having prevailed over the party in deciding the chief minister.
The BJP sources said Modi and Shah had finalised the name of Union minister Manoj Sinha, considered an able administrator.
After Bhartiya Janta Party's massive victory in Uttar Pradesh Assembly election 2017 some names are making the rounds for the position of chief minister of the state.
In choosing Adityanath, Keshav Prasad Maurya and Dinesh Sharma - two leaders from the upper castes and one from the backward caste - the BJP has balanced the caste considerations.
The newly elected Chief Minister of Uttar Pradesh Yogi Adityanath today said the government will work for all section of society without any partiality.
Both MLAs reiterated that equal development of Uttar Pradesh and of every single person of the state along with an end to goonda raj and corruption will remain the topmost priority of Adityanath's government.
After a meeting with local BJP legislators on Saturday, senior party leader M. Venkaiah Naidu announced 44-year-old Yogi Adityanath as Uttar Pradesh's next chief minister.
"This needs to be read in the context of the fact that the BJP did not give even a single ticket to Muslim candidates in the whole of Uttar Pradesh", he said.
In Maharashtra and Jharkhand, neither Devendra Fadnavis nor Raghubar Das was a high-profile leader before they took oath as chief minister.
Defending the lack of Yogi Adityanath's administrative experience, members of his Lucknow unit of the Hindu Yuva Vahini said in Gorakhpur he administers a temple, many hospitals and colleges.
"I want to assure people that BJP, which got votes for development and security, will show positive results soon", the chief minister said.
Priyanka Chaturvedi, a Congress party spokeswoman, tweeted that Adityanath had gone from the fringe of Indian politics to the mainstream, adding that the "mask is truly off" the Modi government.