Party chief Sonia Gandhi approved his admission with immediate effect, AICC General Secretary Janardan Dwivedi said.
Another General Secretary Shakeel Ahmed, who is in-charge of party affairs in Punjab, said several senior state leaders including Amarinder Singh and Pratap Singh Bajwa had pitched for Singh's admission.
Bir Devinder Singh was expelled from the People's Party of Punjab sometime back soon after he had resigned from PPP, citing differences with party supremo Manpreet Singh Badal. He was the chief spokesman of PPP.
Earlier, he was with the Akali Dal and before that with Congress.