Thomas Bartholin (October 20, 1616 - December 4, 1680) was a Danish physician, mathematician and theologian. He is best known for his discovery of the lymphatic system in humans. His discovery was made at about the same time as Olof Rudbeck, though Thomas Bartholin published the discovery first. Jean Pecquet had already noted the lymphatic system in animals.

Thomas Bartholin was the second of the six sons of the physician and Copenhagen professor Caspar Bartholin and his spouse Anne Fincke. The Bartholin family became famous as a family of scientists, twelve of whom became professors at the University of Copenhagen.

Thomas Bartholin's father Caspar Bartholin published the first collected anatomical work in 1611. This work was later illustrated and revised by Thomas Bartholin, becoming the standard reference on anatomy.

In 1663 Bartholin bought Hagestedgaard ("chin-place-farm"), which burned down in 1670 including his library, with the loss of many manuscripts. King Christian V of Denmark appointed Bartholin as his physician with a substantial salary and freed the farm from taxation as recompense for the loss. In 1680 Bartholin's health failed, the farm was sold, and he moved back to Copenhagen, where he died. He was buried in Vor Frue Kirke (Our Lady Church).

The Bartholinsgade, a street in Copenhagen, is named for the family. Nearby is the Bartholin Institute (Bartholin Institutet).