Jain was made vice-president of the party after joining.
"I wanted to do social service. While I was serving that time too I worked for the betterment of poor. I will try to expand the party," Jain said after formally joining the party here in the presence of Athawale.
He had resigned from IPS in February.
"We have entrusted him with the responsibility of vice-president in the party. His joining the party will benefit us," Athawale said.
RPI had rallied behind Devyani when the controversy was at its peak.
"We were in talks with Khobragade. But he has not replied to us in affirmative. We want all supporting the ideology of Ambedkar to join us," Athawale said.