Governor E S L Narasimhan administered the oath to Subhashan Reddy at a brief function at the Raj Bhawan this morning.
Reddy had served previously as Chief Justice of Madras and Kerala High Courts.
He also served as Chairman of Andhra Pradesh State Human Rights Commission.
He will hold the Lokayukta post for five years, as per a notification issued by the state government.
Chief Minister N Kiran Kumar Reddy, acting Chief Justice of High Court Chandra Ghose and others attended the Lokayukta's swearing-in ceremony.