The son of an Irish immigrant farmer who lost his parents at an early age, Noonan served in the Spanish American War from 1898 to 1899. In 1901 he joined the St. Louis chapter of the International Brotherhood of Electrical Workers (IBEW). In 1902 he became president of the local chapter; two years later he was elected international vice president and, in 1919, he was elected IBEW president. He continued to live in St. Louis even though his office was in Washington. In 1922 he was chosen as the fifth vice president of the Building Trades Department of the American Federation of Labor, and in 1924 a member of the Executive Committee of the AFL.

As an authority on electric power, he was sent to the World Power Conference in London in 1924. As the only American delegate, he presented a paper on "Labor´s Part in Power Production". In 1924 he was also appointed by Secretary of Commerce Herbert Hoover to the St. Lawrence Waterway Commission.