Reddy was administered the oath of secrecy by Goa Governor B V Wanchoo in the presence of State Chief Minister Manohar Parrikar.
The opposition MLAs remained absent at the swearing-in ceremony.
"I am visiting Goa after 19 years. I don't know a single individual here. I met the Governor and the Chief Minister for the first time," Reddy told reporters.
"I shall, to the best of my ability, serve Goa through judicial process of which I am part for the last 42 years," the former Supreme Court judge said adding he would take couple of weeks to start working.
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Chief Minister Manohar Parrikar who met the Lokayukta after the swearing-in ceremony also said that it was his first meeting with Reddy.
"I had not even seen his photograph earlier...It was yesterday that I saw his picture in newspapers," said Parrikar who has been accused of appointing his "Yes Man" on the Chair by the opposition parties.
Opposition leaders belonging to Congress and NCP protested on the road leading to Raj Bhavan, where the swearing-in ceremony took place.
The protesters carried black flags and a big banner accusing Reddy of being a "Yes Man".
Although Congress did not formally boycott the swearing-in, Leader of Opposition Pratapsingh Rane, who was on the committee that selected Reddy for the post, was not present at the ceremony.