Mr Saini, 58, acquitted former telecom minister A Raja, DMK MP Kanimozhi and 15 others, including top corporate executives, in the 2G cases while holding that it was not a scam.
Hailing from Haryana, Mr Saini started his career as sub-inspector in Delhi Police in the early 1980s and was selected in Delhi judicial services after clearing a competitive exam.
He shot to fame when as a special judge, he dealt with the sensitive Red Fort attack case and awarded death sentence to the main accused and varying jail terms to others.
According to sources in intelligence agencies, the 'Y' category security cover has been provided to the judge for the threat extended to him by one of the convicts in the Red Fort case.
Known as a tough judge with a sound knowledge of the law, Mr Saini was handpicked to handle the sensitive cases arising out of the 2G spectrum allocation probe.
The 2G case, which started in February 2011 after Mr Raja was arrested by the CBI, witnessed a long journey of nearly seven years.
Apart from the 2G and Red Fort attack cases, Mr Saini also dealt with other high-profile matters, including the 2010 Delhi Commonwealth Games cases, corruption cases against several top government officials.