Thomas Bartholin (October 20, 1616 - December 4, 1680) was a Danish doctor, mathematician and theologist. He is most known for his discovery of the lymph-vessel-system in humans. This discovery was made at about the same time as Olof Rudbeck, though Thomas Bartholin publicised the discovery first. The discovery followed after Jean Pecquets discovery of the lymph-vessel-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 was later famous as a family of scientists, as it created 12 people total that since became professors at the University of Copenhagen.

Thomas Bartholin's father Caspar Bartholin published in 1611 the first collected anatomical work. This work was later illustrated by Thomas Bartholin and revised including the latest knowledge. The book became authoritative about anatomy.

In 1663 he bought Hagestedgaard (chin-place-farm), which burned down in 1670 including his library, where many manuscripts got lost in the fire. King Christian the 5th declared following Bartholin as his life-doctor with a good pay and gave the farm tax-freedom as a plaster on the wound for the loss. In 1680 his health slipped so much, that the farm was sold and Thomas Bartholin moved back to Copenhagen, where he died. He was buried in Vor Frue Kirke (Our Lady Church).

The Bartholin family has gotten a street called after itself in Copenhagen - Bartholinsgade, 1356 København K. (Bartholin street, 1356 Copenhagen K.) In related connection to this lies Bartholin Institutet (the Bartholin Institute).