Former JD(U) leader Ajay Alok, a regular on TV debates, joined the BJP on Friday in the presence of Union minister Ashwini Vaishnaw.
Joining the BJP is like coming to a family, Mr. Alok said, vowing to contribute to the "Modi mission".
The country is today moving in the same direction as the Prime Minister, he told reporters.
He has been a strong defender of the BJP's policies and is seen by the party as a sharp and articulate voice.
He was expelled by the JD(U), the ruling party in Bihar, last year as it believed him to be close to R.C.P Singh, the party's former president who quit following a fallout with its supreme leader and Chief Minister Nitish Kumar.
Mr. Vaishnaw lauded Mr. Alok's contribution and praised him as a sharp analyst.
Mr. Alok took a swipe at Mr. Kumar, saying he is an architect who is destroying his own work by compromising on law and order, corruption and communalism.
