He was active in mining in Arizona, Colorado, Montana, and Nevada, during which time he met Wyatt Earp.

Mahoney was appointed to the Department of Social Security and Public Welfare in 1937 and later served as its chair before resigning in 1952.

[2][3] He married Alice M. Fitzgerald, with whom he had four children including William P. Mahoney Jr., on June 30, 1915, at St. Mary's Church.

[2][8] Mahoney spent his time working in the mines in Cripple Creek, Colorado, Butte, Montana, Tonopah, Nevada, and several locations in northwest Arizona in the 1900s.

[13][14] Mahoney accepted a job as a divisional special agent for the Santa Fe Railroad in December 1926.

[3][16] During the 1932 presidential election, Mahoney was the security expert assigned to meet the train carrying Franklin D. Roosevelt to Arizona.

[3][18] On the day Arizona became a state, February 14, 1912, Mahoney was among those who accompanied Governor George W. P. Hunt on his walk to open the new capitol.

[23][24][25][26] He ran for the position of sheriff in Mohave County in the 1918 election and won the Democratic nomination against Asa F. Harris before defeating Republican nominee J.N.

[42][43] He was appointed by Governor Ernest McFarland to serve on the Arizona Employment Security Commission in 1955.