Ness was born in Chicago, the son of Norwegian bakers. He was educated at the University of Chicago, graduating with a degree in business and law. He began a career as a credit investigator and also returned to university to take a course in criminology, eventually gaining a masters in criminology. In 1927 Ness joined the Treasury Department, working with the 300-strong Prohibition Bureau in Chicago.
Following the election of President Herbert Hoover, Andrew Mellon was specifically charged with bringing down Al Capone. The federal government approached the problem from two directions—income tax evasion and the Volstead Act. Ness was chosen to head the operations under the Volstead Act, targeting the illegal breweries and supply routes of Capone.
With corruption among law-enforcement agents endemic, Ness went through the records of all the treasury agents to create a reliable team, initially of fifty, later reduced to fifteen and finally to just nine men. Raids against stills and breweries began immediately; within six months Ness claimed to have seized breweries worth over $1 million. The main source of information for the raids was an extensive wire-tapping operation.
An attempt by Capone to bribe Ness' agents was seized on by Ness for publicity, leading to the media nickname "The Untouchables". There were a number of assassination attempts on Ness and a close friend of his was killed.
The efforts of Ness and his team had a serious impact on Capone's operations, but it was the income tax evasion which was the key weapon. In a number of federal grand jury cases in 1931, Capone was charged with 22 counts of tax evasion and also 5,000 violations of the Volstead Act. On October 17, 1931 Capone was sentenced to eleven years, and following a failed appeal he began his sentence in 1932.
Ness was promoted to Chief Investigator of the Prohibition Bureau for Chicago and in 1934 for Ohio.
Following the end of Prohibition in 1935, he took a job with the local government of Cleveland as Director of Public Safety. He headed up a campaign to clean out the corrupt police and fire departments, and also tackle illegal gambling and other entertainments. After some notable successes he resigned in 1942, following a drunken car accident.
Ness then moved to Washington, D.C and worked for the federal government. In 1944 he left to become chairman of the Diebold Corporation, a security safe company based in Ohio. He ran unsuccessfully for mayor of Cleveland in 1947 and was forced from his job at Diebold in the same year. He eventually came to work for North Ridge Industrial in Coudersport, Pennsylvania. His book, The Untouchables, was published in 1957 shortly before his death due to a heart attack.
A number of television serials and films have been made (loosely) based on his life, inflating the image of Ness into the fearless incorruptible lawman of legend.
He was married three times, divorcing twice, and had only one child, by adoption.