Microsoft co-founder Bill Gates and former UN chief Kofi Annan have written to a US Judge in support of India-born Rajat Gupta, who will be sentenced on October 24 for insider trading, highlighting his philanthropic work.

Gupta, the most high-profile Wall Street executive convicted of insider trading, will be sentenced by US District Judge Jed Rakoff.

"I know most personally that the poor of the world have a profoundly capable and articulate advocate in Rajat Gupta," Gates said in his letter.

The Microsoft founder said he had worked with Gupta when the Goldman executive had served as chair of the Global Fund to Fight AIDS, Tuberculosis and Malaria.

Gates said while he was "not in a position to comment on any of the particulars of the case against him," he wanted to lend his voice "to round out Rajat's profile as you consider the appropriate sentence for him.

"Many millions of people are leading better lives - or are alive at all - thanks to the efforts he so ably supported," Gates said in his letter.

Annan said Gupta had worked on many projects with him, including one on management reform at the UN in which Gupta was an adviser.

"I came to respect his judgement, and we became good friends," the former UN Secretary General, Kofi Annan, said in his letter.

"I urge you to recognise Rajat for the good he has done in the world, to give him the credit that he deserves for helping others and to take into account his efforts to improve the lives of millions of people," he said.

Gupta faces a maximum sentence of 25 years.

The India-born ex-McKinsey head was found guilty by a Federal jury in June this year of passing confidential company information about Goldman Sachs to hedge fund founder and close business associate, Raj Rajaratnam.

Letters by Gates and Annan are among the more than 200 that have been sent to the judge.

India-born Ajit Jain, a top Berkshire Hathaway executive and possible successor to Warren Buffett, has also written to judge Rakoff in support of Gupta.

Jain said in his letter that the impression of Gupta at his trial of someone who abused his position "for personal gain or aggrandisement" is "wholly inconsistent with the character of the man I know".

"On no occasion of our meetings did Rajat ever seek to inappropriately obtain or leverage information," he wrote, adding that Gupta "has already paid a terrible price" and "been disgraced personally and professionally".

Jain said in the years that he has known Gupta socially, "he customarily chided me to become more active in philanthropic causes."

"I suspect that there are more meaningfully redemptive possibilities for Rajat than a substantial period of incarceration," Jain, who had earlier testified as a defence witness by videotape at the trial, said in his letter.

Many letters have been written by company heads, academics, friends and family, including his wife and four adult daughters.

"I know I have to accept the decision of the jury but I cannot but feel that who my husband is and what he stands for did not fully come out at the trial," Gupta's wife, Anita said in her letter to the judge.

Corporate leaders in India, including Reliance Industries Chairman Mukesh Ambani, Godrej group head Adi Godrej, and Ajit Rangnekar, dean of the Hyderabad-based Indian School of Business which Gupta had co-founded, had also written letters in support of Gupta ahead of the trial.