Thakur reached the DGP office in the afternoon with his order of reinstatement.
"I have formally joined from today after I got the orders regarding the same yesterday," Thakur told PTI.
Thakur was reinstated with effect from October 11, 2015 with full salary benefits as directed by the Lucknow bench of the Central Administrative Tribunal (CAT).
"The order dated May 11, 2016 of Principal Secretary (Home) Debashish Panda says, the Central government has quashed the suspension through its order dated March 31, 2016 which was again reiterated by the Lucknow bench of CAT on April 25, 2016," said Thakur.
Thakur, who had alleged that he was threatened by ruling SP chief Mulayam Singh Yadav, was suspended by the state government in July, 2015.
The IG-level officer was put under suspension when he had approached the Union Home Ministry in Delhi, seeking a CBI probe into a rape case filed against him after he had lodged a complaint against Mulayam for threatening him.