Wiesel, who was born at Uppsala in Sweden, obtained his MD from the Karolinska Institute, Stockholm. He moved to America shortly afterward, working first at Johns Hopkins before moving to Harvard (1959), where he was appointed professor of neurophysiology in 1974. In 1983 he moved to Rockefeller University, New York, where he served as head of the neurobiology laboratory.

Since his arrival in America Wiesel has been engaged upon a most productive investigation with David Hubel, into the mammalian visual system. Their 20-year collaboration led to the formulation of the influential hypercolumn theory. Wiesel and Hubel received the 1981 Nobel Prize for physiology or medicine for their work, sharing the prize with Roger Sperry. Wiesel has gone on to investigate the chemical transmitters involved in the nerve cells of the visual system.