Singh who was elected from the Rajakhera assembly seat took the oath in Hindi at Raj Bhawan.
Chief Minister Vasundhara Raje, her cabinet colleagues, former Congress Chief Minister Ashok Gehlot and other MLAs were present at the brief oath-taking ceremony.
An eight-time Congress legislator, Singh will administer oath to remaining 199 members in the House beginning tomorrow.
Earlier, three other MLAs - Sunderlal, Ghanshyam Tiwari, and Narayan Singh - have been appointed to assist Singh in the House during the oath-taking of MLAs.