Singh was administered the oath of office by Governor K K Paul at Raj Bhawan auditorium in the presence of Chief Minister Harish Rawat.
Prominent among those who attended the swearing-in was BJP MP from Haridwar Ramesh Pokhriyal Nishank, Mussoorie MLA Ganesh Joshi, Uttarakhand's new Chief Secretary S Ramaswamy and DGP M A Ganpati.
A 1983-batch IAS officer, Singh had recently taken voluntary retirement from the post of Chief Secretary before his superannuation in December this year.
The CIC's post was laying vacant for a year since N S Napalchayal stepped down in 2015 after completing his five-year term.