"I am thankful to Governor Ram Naik who invited me to form government in UP," he said in his first brief media interaction at Raj Bhawan.
Adityanath said he would follow Prime Minister Narendra Modi's slogan "sab ka saath, sab ka vikas" (With all and development of all) and ensure all round development of the state.
"I am confident that the state will march on the path of development," he said.
He thanked party MLAs for reposing faith in him.
The 44-year-old five-term MP from Gorakhpur was earlier in the day elected the BJP legislature party leader at a meeting of the newly elected MLAs, a week after BJP won a resounding three-fourth majority in the key Hindi heartland state, making a comeback to power after 15 years.