Chief Justice of Rajasthan High Court Sunil Ambwani administered the oath of office to Singh, 82, at a ceremony held at Raj Bhawan here.
Before that, Chief Secretary Rajiv Mehirshi read out the warrant of appointment issued by the President.
Assembly Speaker Kailash Meghwal, Chief Minister Vasundhara Raje and senior officers were present on the occasion.
Enthusiastic party workers shouted slogans 'jai shree ram' and 'vande matram' when Singh was taking the oath. He was also given a guard of honour.
U P Governor Ram Naik was holding the additional charge of Rajasthan before the appointment of Kalyan Singh.