Born at Ryazan in Russia, Pavlov studied medicine and general science at the University of St. Petersburg and the Military Medical Academy. He subsequently carried out research in Breslau (now Wrocław, in Poland) and Leipzig (1883–86). Returning to St. Petersburg, he became professor of physiology at the Medical Academy and director of the physiology department of the Institute of Experimental Medicine.

Pavlov's early research lay in the physiology of mammalian digestion, showing, for example, that the secretion of digestive juices in the stomach is prompted by the sight of food and nerve stimulation via the brain. For this work Pavlov received the Nobel Prize for physiology or medicine (1904). He then went on to study the way that dogs and other animals may be induced to salivate and show signs of anticipation of food by actions, such as the ringing of a bell or even a powerful electric shock, that they have learned to associate with the appearance of food. Pavlov's work on conditional or acquired reflexes, which he believed to be associated with different areas of the brain cortex, has led to a new psychologically-oriented school of physiology and has stimulated ideas as to the probability of many aspects of human behavior being a result of ‘conditioning’.

Pavlov openly criticized communism and the Soviet government. In 1922 he requested and was refused permission to move his laboratory abroad. Following the expulsion of priests' sons from the Medical Academy, Pavlov, himself the son of a priest, resigned from the chair of physiology in protest. Despite such actions his work continued to be supported by state funds and Pavlovian psychology remained popular in the Soviet Union.