[3] After graduating college, he went to Cananea, in northern Sonora, where he ran a restaurant and worked for the Southern Pacific Railroad.
[2] He moved to Arizona in 1905, settling in Patagonia, and two years later began working for the Alvarado Gold Mining Company.
[2] In August 1916 O'Neil was a candidate seeking one of the seven seats from Cochise County in the Arizona House of Representatives,[8] and was one of the seven Democrats selected in the primary.
[9][10] In 1918 he was one of three candidates running in the Democrat's primary for the two seats from Cochise County in the Arizona State Senate.
[11] O'Neil and T. A. Hughes, both of whom had served in the House during the previous term, became the Democrat's candidates.
[20] In May 1934 O'Neil announced his intention to run in the Democrat's primary, seeking a full term on the tax commission.
[21][22] During the primary election in 1934, O'Neil was falsely accused as being part of the Bisbee Deportation event in an attempt to discredit him.
[30] He ran unopposed in the primary, and defeated Republican F. M. Wilkinson in November's general election.
[36] His opponent in the Democrat primary was former commissioner and Tax Commission chairman Thad Moore.