Miffed Sharief, who was denied the party ticket to contest elections told a news channel, "Sonia is the reason I quit the party".
83-year-old Sharief, who was considered as one of the "secular" faces of the party and one of the biggest names among the leaders from the minority community, snapped his six-decade-old association with Congress.
"I have faxed my resignation from the Congress primary membership to AICC President Sonia Gandhi, but will not contest Lok Sabha elections," Mr Sharief said last month.
A seven-time Lok Sabha member, whose claim for ticket from Bangalore Central was overlooked in favour of Youth Congress wing chief Rizwan Arshad, did not share contents of his letter.
Asked whether he would join JD(S) to contest the April 17 Lok Sabha elections, Mr Sharief said he does not want to be associated with one party and work within the framework of it.
"However, I am ready to work for secular parties," he said.
On whether he will campaign for JDS, the former Union minister said, "Yes I would."
On March 14, Sharief had indicated he was keeping open the option of joining JDS after Congress plumped for Riawan Arshad for Bangalore Central seat.
Sharief had earlier written to the UPA Chairperson Sonia Gandhi not to field any candidate against JDS supremo DeveGowda, raising many an eyebrow in Congress.