External affairs minister S M Krishna resigned on Friday ahead of the reshuffle of the Union Cabinet scheduled on Sunday.
The 80-year-old leader from Karnataka is believed to have sent his resignation to Prime Minister Manmohan Singh in the afternoon, sources said.
Indications are that with the assembly elections due before next May in Karnataka, the former chief minister may be given a party assignment in the state.
The resignation is also a clear indication that the Union Council of Ministers is set for a revamp on Sunday with the induction of new faces considered close to Rahul Gandhi and elevation of some young ministers of state.
Whether Gandhi himself would join the government or not was still a matter of speculation though sources say that sometime back he was inclined towards such a possibility.
Krishna was made the external affairs minister immediately after the elections in 2009 when UPA came back to power for the second time. His name has been part of the speculation whenever there was speculation about a Cabinet reshuffle.
The possible names of the successors in the external affairs ministry include commerce minister Anand Sharma.
The other changes, expected to take place on Sunday, could include ministers holding dual portfolio shedding one of their responsibilities.
Actor-turned-politician Chiranjeevi may be inducted into the ministry as a reward for his help in ensuring the stability of Congress government in Andhra Pradesh with support of his 18 MLAs.
It is no secret that Prime Minister Manmohan Singh is keen to have Rahul Gandhi inducted into his Cabinet but so far the young MP was not not inclined as he was focused on building the Congress organisation, especially the youth wing. Another proposal making the rounds is that Gandhi may be elevated from being a general secretary to the revived post of working president.
The Congress is said to be working on more measures to reach the 'aam aadmi' (common man) on the lines of the NREG scheme which had paid rich dividends to the party in the last elections.
Younger ministers like Sachin Pilot and Jyotiraditya Scindia are likely to be promoted and may get independent portfolios. There has been speculation about a reshuffle in the Cabinet for quite some time now, especially after the exit of Trinamool Congress ministers both at the levels of Cabinet and ministers of state levels.