BJP president J P Nadda also appointed former Congress spokesperson Jaiveer Shergill its national spokesperson, the party said in a statement.
Singh (80) also merged his newly formed Punjab Lok Congress (PLC) with the Bharatiya Janata Party (BJP).
Singh, the scion of the erstwhile Patiala Royal family and a two-time chief minister, had floated the PLC after he quit the Congress following his unceremonious exit as the chief minister last year.
Punjab votes for change but will AAP and Mann live up to the expectations of the state, which is the food bowl of India.
Assembly elections in Punjab are expected to be held early next year.
Amarinder, who named his political party as the Punjab Lok Congress, is hoping for a seat arrangement with the BJP for the upcoming elections.
Narendra Modi has announced that the government will repeal three controversial farm laws, which were at the centre of protests by farmers.
The Punjab Lok Congress will be formally launched after the Election Commission registers it and allots a poll symbol.
The development comes just months ahead of the Punjab assembly elections.
He said he would soon announce the launch of his own political party to serve the interests of the people, including the farmers who've been fighting for their rights for over a year now.