Born in Charleston, South Carolina, Maybank attended the public schools and graduated from Porter Military Academy and from the College of Charleston. He served in the United States Navy during World War I, and engaged in the cotton export business from 1920 to 1938.

Maybank was an alderman of Charleston from 1927 to 1931, and mayor of Charleston from 1931 to 1938. In addition, hee was a member of the South Carolina State Advisory Board of the Federal Administration of Public Works from 1933 to 1934, and chairman of the South Carolina Public Service Authority from 1934 to 1939. He was also a member of the Board of Bank Control from 1933 to 1934. After all this, Maybank became the governor of South Carolina from 1939 to 1941.

On September 30, 1941, Maybank was elected as a Democrat to the United States Senate to fill the vacancy caused by the resignation of James F. Byrnes. He was reelected in 1942 and 1948, and served in all from November 5, 1941 until his death in 1954. While in the Senate, Maybank served as chairman of the Committee on Banking and Currency and as co-chairman of the Joint Committee on Defense Production. He died at his summer home in Flat Rock, North Carolina, and was interred in Magnolia Cemetery in Charleston.

{{succession box | title = Chair, United States Senate Committee on Banking, Housing, and Urban Affairs| before = Charles W. Tobey| after = Homer Capehart| years = 1949 - 1953