Mehrishi, 62, was administered the oath of office by President Ram Nath Kovind at Rashtrapati Bhavan. Vice President M. Venkaiah Naidu and Prime Minister Narendra Modi were also present on the occasion.
A 1978 batch (retired) Indian Administrative Service (IAS) officer of the Rajasthan cadre, Mehrishi completed his two-year fixed term as the home secretary last month.
Mehrishi will have tenure of about three years.
He also possesses Master of Arts (MA) and Bachelor of Arts (BA) degrees from Delhi University.
The CAG is appointed for a term of six years or till the incumbent attains the age of 65 years, whichever is earlier. (ANI)