Accompanied by his son, Radadia visited the legislative assembly and submitted their resignations to Speaker Vaju Vala.
They later drove to Ahmedabad, where the state Congress headquarters is located, and put in their papers.
A former MP, Radadia, is a strong Leuva Patel community leader from Saurashtra. He was at the centre of a controversy when he was caught brandishing a gun at a toll plaza in Karzan in Vadodara district after being asked to show his identity card.
"I have tendered my resignation to protest negative policies of the Congress against the state of Gujarat. The Congress culture is of favoritism," Radadia said after submitting his resignation as MLA.
"I have submitted my resignation from the Congress and also as an MLA so that I can join BJP," he said in reply to a question and showered praise on Chief Minister Narendra Modi.
"Modi has brought Gujarat to new heights of development and he is the prime ministerial candidate of BJP," he said.
Vitthal Radadia, who had resigned as MP and decided to continue as MLA after the recent state Assembly elections, was upset over not being made Leader of the Opposition, the post which went to party veteran and former chief minister Shankarsinh Vaghela.
Radadia, is a powerful figure in state's co-operative sector and has strong support base among farmers of Saurashtra.