Tunnell taught in the public schools, eventually becoming principal of the schools at
Frankford,
Selbyville and
Ocean View in Delaware. Meanwhile, he studied the law, was admitted to the bar in 1907 and began a practice in Georgetown. He was president of the Georgetown Board of Education from 1919 until 1932. Tunnell was also a banker and owned and operated a number of farms in Sussex County. Tunnell first ran for a seat in the United States Senate in 1924, but was defeated by Republican
T. Coleman du Pont. He was elected to the United States Senate in 1940, this time defeating the incumbent Republican Senator John G. Townsend Jr. During this term, he served with the Democratic majority in the 77th, 78th, and 79th congresses. He was chairman of the Committee on Pensions in the 78th and 79th congresses. Tunnell lost his bid for a second term in 1946 to Republican
John J. Williams from Millsboro, Delaware. He served from January 3, 1941, to January 3, 1947, during the administrations of U.S. presidents
Franklin D. Roosevelt and
Harry S. Truman. Director of the
Farmers' Bank of Delaware (1905–1957) Tunnell was an early supporter of the
Equal Rights Amendment. ==Death and legacy==