Singh had played a key role in the arrest of BJP leader Lal Krishna Advani during the Ram Temple movement in 1990 while he was posted in Bihar that had led to the fall of the then VP Singh government following withdrawal of support by BJP.
RK Singh is likely to contest the next LS polls from Bihar
Lalu Prasad, the then Chief Minister of Bihar, had ordered Advani's arrest in Samastipur on October 23, 1990. Singh, a 1975 batch IAS officer of Bihar cadre, had retired as Home Secretary on June 30.
He will join BJP in presence of BJP president Rajnath Singh, former Union Minister and MP from Bhalgalpur Shahnawaz Hussain and former Bihar Deputy Chief Minister Sushil Modi, party's Bihar-incharge Dharmendra Pradhan and Rajya Sabha MP Rajiv Pratap Rudy.
Singh is likely to contest from either Arra or Supaul Lok Sabha constituency in Bihar, sources said.