Former prime minister Manmohan Singh and Congress president Sonia Gandhi on Monday met P Chidambaram at Tihar Jail, and expressed concern over his continued detention in custody.
Singh said he hoped the courts would render justice in Chidambaram's case.
Chidambaram, a former Union finance minister, was arrested on August 21 by the Central Bureau of Investigation for alleged corruption in the grant of Foreign Investment Promotion Board clearance in the INX Media case.
He was later remanded in judicial custody and sent to Tihar Jail on September 5.
Singh said no decision in the country was taken by a single person and wondered how a minister simply approving recommendations can be accused of committing a crime.
He feared that if a minister is liable for approving a recommendation, the whole system of government in the country will collapse.
"We are concerned with continued detention in custody of our colleague P Chidambaram," Singh said in a statement after meeting Chidambaram.
"We are confident, and we sincerely hope, that the courts will render justice in this case," the former prime minister said in the statement.
Singh said in the country's system of government, no decision can be taken by any single person and all decisions are collective decisions recorded in files.
He said a dozen officers, including six secretaries to the government, examined and recommended the proposal and Chidambaram as minister approved the unanimous recommendation.
"If the officers are not at fault, it is beyond our comprehension how the minister who simply approved the recommendation can be accused of committing an offence. If the minister is liable for approving a recommendation, the whole system of government will collapse," he said.
Singh and Gandhi were accompanied by Karti Chidambaram, the former finance minister's son who is also a Lok Sabha MP, during their meeting with Chidambaram.
"I am honoured that Smt Sonia Gandhi and Dr Manmohan Singh called on me today. As long as the Congress party is strong and brave, I will also be strong and brave," Chidambaram's family tweeted on his behalf and said he was honoured that the two leaders visited him.
He also took a dig at Prime Minister Narendra Modi over his "everything is fine in India" remark, saying, "Bharat mai sab achha hai. Except for unemployment, loss of existing jobs, lower wages, mob violence, lockdown in Kashmir and throwing Opposition leaders in prison."
The prime minister at the 'Howdy, Modi' event in Houston on Sunday said, "Energy of NRG (stadium) is a witness of synergy between India and the US... My answer to 'Howdy, Modi' is only this: Everything is Fine in India".
Karti Chidambaram expressed his gratitude to the two Congress leaders for meeting his father.
"My father and I are extremely grateful to Congress president Sonia Gandhiji and former prime minister Manmohan Singhji for visiting us today. This will give us the strength and support in this political fight," he said.
The meeting lasted for the full allotted time of around half-an-hour, sources said.
The party "fully" stands behind Chidambaram and will fight the case politically, the sources quoted Gandhi as having said during the meeting.
Chidambaram also discussed at length with Singh the corporate tax cut and GST concessions announced by the government, according to the sources.
The two held detailed discussions on these economic issues and their repercussions on the country's economy, they said.
According to the sources, it was discussed during the meeting that the revenue loss due to the tax relief would not be Rs 1.4 lakh crore, as claimed by the government, because all corporates do not pay corporate tax at the highest rate.
The visiting leaders also enquired about Chidambaram's health and welfare, they said.
Congress senior spokesperson Anand Sharma called it a "weird statement" when asked about the BJP's accusation that the Congress is "standing behind corruption".
He said the Indian laws are clear that till the time anyone is found guilty in the court, the accused is innocent.
They are only accused and they have constitutional rights to speak out and get bail, Sharma said.
"Those who are in jail for serious offences, their family and close friends also meet them in jail. It is surprising that even family members of BJP leaders, who were in jail, have been going to meet them.
"Chidambaram is a senior Congress leader, he has been a former finance minister for a long time, a former Home minister of India, and Sonia Gandhi and the former PM went to meet him, I think no one should have objections to it," Sharma said.
Senior Congress leaders Ghulam Nabi Azad and Ahmed Patel had also met P Chidambaram at Tihar Jail last week.