When asked by reporters what prompted him to sever his ties with Congress, the former deputy chief minister said, "It is improper that senior leaders of Congress like me were kept in the dark in ticket allocation and I felt insulted and decided to join BJP".
Amin is in Rajkot to participate in election campaign on behalf of the ruling BJP.
When asked whether chief minister Narendra Modi, who is also the president of Gujarat Cricket Association (GCA), has promised him any post in the organisation, Amin replied in negative, saying he joined BJP "without any expectation".
Seeking to punch holes in the Congress' claims, Amin said, "Congress' promises of giving laptops to students and free treatment to patients suffering from heart and kidney ailments, are impracticable and a poll gimmick".
Elections will be held in Gujarat in two phases on December 13 and 17.
Amin's entry into the BJP is expected to boost its prospects in the Saurashtra region where renegade saffron party leader and former chief minister Keshubhai Patel's newly launched Gujarat Parivartan Party (GPP) is putting a stiff challenge to Narendra Modi.