Yadav, who had been a close aide of RJD chief Lalu Prasad, joined BJP in the presence of party president Rajnath Singh and senior leaders from Bihar including Ravi Shankar Prasad.
Welcoming him into the party fold, Rajnath Singh said Yadav has been RJD's secretary general for the last 17 years and had decided to support the BJP.
Expressing his gratitude to the BJP leadership for accepting him into the party, Yadav said he will work for the party not as a leader but as a worker, which he has been for the last 35 years of his political life.
Yadav, a former legislator and a Rajya Sabha MP, accused Lalu Prasad of "promoting" his family over his party workers, who he said, were feeling stifled.
"RJD has moved away from its core values. Lalu gave precedence to his family over party and cadres. I was in a dilemma on what to do for the last few days and then decided to quit the party and join BJP for the sake of giving social justice," he said.
"I have never been a leader. I have been a common worker in my 35 years of working in the RJD. The RJD workers in Bihar are feeling suffocated as family is being given importance. I felt social justice should be taken forward and not family justice," Yadav said in the presence of top BJP leadership.
Ram Kripal Yadav is keen to contest from the Pataliputra seat on which the RJD has fielded Lalu's daughter Misa Bharti.