Born in the Lower East Side, Tanahey was a member of the Tammany Hall political machine, serving under boss Tom Foley and holding appointed posts in the early 20th century before becoming alderman.
Popular but in poor health, Tanahey was considered a possible Tammany leader of the 1st district after Foley's 1925 death but yielded to colleague Peter J. Hamill.
Foley was the local leader of the Tammany Hall political machine that catered to the working class, especially Irish immigrants, and held picnics for lower- and working-class families.
[3] Tanahey began serving office around 1908, as chief clerk of the New York State Labor Department and later an assistant government appraiser in President Woodrow Wilson's administration.
[8] One of Foley's most intimate friends was tax commissioner John F. Gilchrist, who was an easy choice as the new leader but declined the position.
Tanahey and Assemblyman Peter J. Hamill emerged as the two major candidates of the contest, which attracted more interest than usual as it was in Smith's home district.
[10] At the time of the 1928 presidential election, where Smith would become the Democratic nominee before losing to Republican Herbert Hoover, New York's 1st congressional district was split between Lower Manhattan and Staten Island.
He introduced a bill in 1926 to provide for credit in "paid service" rather than civil service to the federal government, an act incidentally found ultra vires by a decision of New York Supreme Court judge Joseph M. Proskauer invalidating ex-mayor John F. Hylan's pension.