Elwyn Thomas was born in Eldred, Florida, a small community in St. Lucie County named after his mother's family, on July 5, 1894, to Hal S. Thomas and Julia E. Thomas. He attended Stetson University College of Law in DeLand, Florida where he received his LL.B degree in 1915. He was admitted to law practice in Florida the same year. He began his practice in DeLand and later moved to Fort Pierce. In 1917, he became the prosecuting attorney for St. Lucie County. Two years later, he served as the City Attorney for both Vero Beach (1919–1923) and Fort Pierce (1919–1925). On June 14, 1924, he married Eva Banes. In 1925, he became the 21st Circuit Court Judge for St. Lucie County, a position he held for ten years.
From 1935-1936, he was the president of the Fort Pierce/St. Lucie County Chamber of Commerce. From 1935 to 1938, he also served as Senior Judge of the 9th Judicial Circuit. In 1938, he was appointed to the Florida Supreme Court as an Associate Justice and he served on Florida's high court for 31 years. From 1947 to 1949 and from 1959 to 1961, he served as Chief Justice of the Florida Supreme Court. Stetson University awarded him an Honorary Doctor of Laws degree in 1951. Justice Thomas was instrumental in creation of the Florida District Courts of Appeal, lobbying for their establishment in 1957.
- Florida Bar Association
- past Master of Ft. Pierce Lodge No. 87
- Phi Alpha Delta Law Fraternity
- Member, David Brewer Chapter, since April 2, 1915
- District Justice, 1954
- Supreme Vice Justice, 1954-1956
- Supreme Justice, 1956-1958
- Chair, Supreme Advisory Board, 1958-1960
- Rotary Club of Tallahassee
- Sigma Nu Fraternity
- Vero Beach Yacht Club
- charter member, 1926
- See Office Website of Florida Supreme Court Archived July 5, 2010, at the Wayback Machine.
- see, “Brief Description” of the Florida District Courts of Appeal at Official Florida Courts Website
- The Reporter, October, 1958. (Quarterly Publication of Phi Alpha Delta Law Fraternity, 1958.)