Born at Halmstad in Sweden, Samuelsson was educated at the Karolinska Institute, Stockholm, where he gained his MD in 1961. He continued to work there until 1966, when he moved to the Royal Veterinary College, Stockholm as professor of medical chemistry. In 1972 he returned to the Karolinska Institute as professor of medicine and physiological chemistry.

Samuelsson has worked extensively on the hormonelike prostaglandins first identified by Ulf von Euler in the 1930s. With Sune Bergström in the 1950s he worked out the structure of several prostaglandins and went on to explore some of their physiological properties. Later work by Samuelsson and his colleagues indicated a relationship between prostaglandins and the chemicals involved in transmitting nerve impulses. He discovered the prostaglandin PGA₂, thromboxane, which causes blood vessels to contract and platelets to clump. A second prostaglandin, PGE₂, inhibits the release of norepinephrine, a neurotransmitter of the sympathetic nervous system, and thereby blocks the transmission of nerve impulses.

Samuelsson also worked out the structure of a number of prostaglandins. They were shown to be closely related and synthesized in the body from a number of polyunsaturated fatty acids. All prostaglandins were found to be 20-carbon carboxylic acids with a five-member carbon ring. They are divided into three series – PG₁, PG₂, and PG₃ – depending on whether they have one, two, or three double bonds. The different prostaglandins could be distinguished by the location of an oxygen atom or an hydroxyl group (OH). For his work on prostaglandins Samuelsson shared the 1982 Nobel Prize for physiology or medicine with John Vane and Sune Bergstrom.