He became involved in politics in 1913, serving as secretary of the North Dakota State Socialist Party until 1916. Teigan moved to Minneapolis, in 1917, where he served as secretary of the National Nonpartisan League from 1916 to 1923. From 1923 to 1925, he was secretary to Senator Magnus Johnson. At that time, he also began working as an editor and newspaper writer. In 1930 he was the Minnesota Farmer Labor Party nominee for state auditor, coming in second with 35.96% of the vote. He continued in newspaper work until 1932, when he was elected to the Minnesota Senate where he served one term.
In 1936, he was elected as a candidate of the Minnesota Farmer Labor Party to the 75th congress. After one term, he failed to win reelection, and was also defeated in a 1940 bid to regain his seat. After leaving congress, he resumed newspaper and editorial work in Minneapolis, until his death on March 12, 1941. He is interred in Hillside Cemetery in Minneapolis. The papers of Henry George Teigan are maintained by the Minnesota Historical Society
in St. Paul, MN.