Thomas Holliday Hicks (September 2, 1798 – February 14, 1865) was a politician in the divided border-state of Maryland during the American Civil War.

Under pressure to call the General Assembly into special session, he held it in the pro-Union town of Frederick, where he was able to keep the state from seceding to join the Confederacy.

In his gubernatorial inaugural address, Hicks criticized the numbers of foreign immigrants coming to America and warned that they would "change the national character".

"[2] Hicks belatedly supported the Union of the states and sought to prevent Maryland from seceding and joining the Confederacy.

But, writing to Lincoln on April 22, 1861, Hicks informed the new president that "I feel it my duty most respectfully to advise you that no more troops be ordered or allowed to pass through Maryland", requested that Lincoln obtain a truce with the South and suggested that Sir Richard Lyons mediate.

The Assembly normally met in Annapolis, but that city was occupied by Union troops, so Hicks changed the location to Frederick, a generally pro-Union town.

In December 1862, his successor as governor, Augustus W. Bradford, appointed him to the U.S. Senate from Maryland following the death of his predecessor, James A. Pearce (D).

Although ill, he campaigned for election to finish the term, winning on January 11, 1864[6] while endorsing Lincoln's reelection in 1864.