Born in Chicago, Illinois, Mahoney was educated in the public schools of Chicago. He engaged in mercantile pursuits in 1876. He was an alderman in the Chicago City Council from 1884 to 1887 and again from 1890 to 1896.
Mahoney was elected as a Democrat to the 57th and 58th Congresses and sat from March 4, 1901, until his death in Chicago on December 27, 1904.[1]