Singh's son Raninder Singh, daughter Jai Inder Kaur, and Congress leader and deputy speaker of Punjab Assembly Ajaib Singh Bhatti have also joined the BJP.
He was discharged from hospital after undergoing spinal surgery on June 27.
Amarinder had earlier said he was ready to reveal the names and give other details of all former ministers and MLAs who were allegedly involved in corrupt activities during his tenure.
The Congress, with which he had a bitter parting just months back, hasn't done too well either in the state, swept by an Aam Aadmi Party wave.
Amarinder Singh appointed five vice presidents and 17 general secretaries for his newly launched political outfit Punjab Lok Congress.