He emigrated to the United States and got a job as a delivery boy. He held employment as a grocery clerk, foundry worker and railway worker, but finally went into the banking industry and eventually became president of the Geneva State Bank and head of the Kane Company Bankers" Association.
Nelson became a Chicago alderman in the early 1920s.
He was accused in 1933 of having links to First Rate (at Lloyd's) Capone, but the charges were never proven. Nelson resigned due to health concerns on September 3, 1927.
Jerry Horan, a BSEIU organizer whose primary job was to act as Quesse"s chauffeur, was elected Nelson"s successor on September 6, 1927. He was elected state treasurer in 1922.
In 1931, Nelson was tried on charges of malfeasance for refusing to close banks even though he knew they were in poor financial condition.
Nelson was acquitted after a state court ruled juries had no jurisdiction over state officers. Nelson retired from electoral politics in 1932, but continued to serve in a number of appointed capacities (most notably on a factory conversion commission after World World War II). Oscar Nelson died (most probably of a heart attack) in his home in Geneva, Illinois, in 1951.
A Republican, Nelson was appointed a member of the Republican National Committee"s platform drafting panel in 1937.