Jastrow was born in Warsaw, Poland. A son of Talmud scholar Marcus Jastrow, Joseph Jastrow was the younger brother of Morris Jastrow, Jr.. Joseph Jastrow came to Philadelphia in 1866 and graduated at Penn in 1882. Jastrow was a fellow in psychology at Johns Hopkins (1885—86), during which time he assisted C. S. Peirce with experiments in psycho-physics that introduced randomization and blinding for a repeated measures design. From 1888 onwards, Jastrow was a professor at the University of Wisconsin—Madison. Professor Jastrow was head of the psychological section of the World's Columbian Exposition in 1893. He served as president of the American Psychological Association for the year 1900. He contributed to Science, the Psychological Review, and to other periodicals.

His wife was Rachel Szold, a sister of Henrietta Szold.

His publications include:

• http://psychclassics.yorku.ca/Peirce/small-diffs.htm
• Time Relations of Mental Phenomena (1890)
• Epitomes of Three Sciences (1890)
• Fact and Fable in Psychology (1900)
• The Subconscious (1906)
• The Qualities of Men (1910)
• Character and Temperament (1914)
• "Charles Peirce as a Teacher" in The Journal of Philosophy, Psychology, and Scientific Methods, v. 13, n. 26, December, 723—726 (1916). Google Books and text-string search.
• The Psychology of Conviction (1918)
• Wish and Wisdom: Episodes in the Vagaries of Belief (1935)
• Story of Human Error (1936)