All three are believed to be close to rebel leader and former Chief Minister Shankersinh Vaghela, who quit as Leader of Opposition on his birthday on July 21, alleging that there was an intra-party conspiracy to oust him from the Congress.
The three submitted their resignations to Speaker Ramanlal Vora on Thursday afternoon.
They later went to the BJP headquarters and joined the party.
Rajput, Chief Whip of the Congress who was rumoured to be planning to contest the Rajya Sabha election against official party nominee Ahmed Patel, political secretary to Congress President Sonia Gandhi, is an MLA from Siddhpur.
Balwantsinh Rajput's daughter is the wife of Vaghela's son Mahendrasinh, an MLA.
Tejashree Patel, a firebrand woman leader and one of the most active legislators of the Congress in the state Assembly, was elected from Viramgam.