A Times Now television channel report late on Thursday evening revealed that a formal announcement of Singh joining the BJP would be made at 4.30 p.m. on Friday.
Singh, a retired Indian Administrative Service officer of the Bihar cadre (1975 batch) was the Union home secretary from July 1, 2011 till June 30, 2013.
He succeeded G K Pillai and has since been succeeded by Anil Goswami.
Our correspondent in New Delhi reports that Singh might be given a ticket to contest the 2014 Lok Sabha elections from the saffron party.
Interestingly, it was Singh -- the district magistrate of Samastipur in 1990 --who arrested senior BJP leader L K Advani while his Rath Yatra was on its way to Ayodhya, on the orders of then Bihar Chief Minister Lalu Prasad Yadav.
Image: RK Singh
With inputs from ANI