He soon became a Postal Inspector himself, and served in that role until 1919,[1] when he was appointed Chief of the Treasury Department's Internal Revenue Service Intelligence Unit.

On July 1, 1919, the Commissioner of Internal Revenue, Daniel C. Roper created the Intelligence Unit to investigate widespread allegations of tax fraud.

Despite attempted jury tampering and death threats against Wilson, Irey's investigation succeeded in the conviction of Capone for tax evasion in 1931.

During the Lindbergh kidnapping, some sources indicate that Irey insisted on tracking the serial numbers on the gold certificates used as ransom money (which ultimately led to the arrest and conviction of Bruno Richard Hauptmann).

After several months awaiting guidance from the new administration, Irey received a go-ahead to restart the investigation from Treasury Secretary Henry Morgenthau Jr.

In his biography, Irey related the personal interest and direct intervention of FDR in the investigation of Long, another of his political enemies who was considering running for president against Roosevelt in 1936.

Irey appears in the opening scene of the 1947 semidocumentary film T-Men, starring Dennis O'Keefe, explaining to the audience how the various enforcement agencies of the Treasury Department work together on the case they are about to see.