Swami, son of late RJD MP Uma Shankar Singh, was welcomed in the BJP-fold by its state unit president Mangal Pandey at a function here.
Swami thanked BJP leadership for accepting him and said that he would strive hard to ensure BJP candidates' victory in Saran, Gopalganj and Maharajganj parliamentary seats.
Swami unsuccessfully contested the bypoll for Maharajganj parliamentary seat on a Congress ticket after his father's death last year.