The Cardinals went 70-92 during the season and finished 6th (and last) in the National League East division, 25 games behind the NL East champion Pittsburgh Pirates. It was one of the few times that the Cardinals had finished in last place, and the first, and only time that it has happened since 1918.
- November 28, 1989: Bryn Smith was signed as a free agent by the Cardinals.
- November 30, 1989: Danny Cox was signed as a free agent by the Cardinals.
- December 6, 1989: Jim Lindeman and Matt Kinzer were traded by the Cardinals to the Detroit Tigers for Bill Henderson (minors), Marcos Betances (minors), and Pat Austin (minors).
- February 27, 1990: Alex Cole and Steve Peters were traded by the Cardinals to the San Diego Padres for Omar Olivares
April 23, 1990: John Costello was traded by the Cardinals to the Montreal Expos for Rex Hudler.
May 4, 1990: Tom Brunansky was traded by the Cardinals to the Boston Red Sox for Lee Smith.
May 5, 1990: Terry Francona was signed as a free agent by the Cardinals.
July 2, 1990: Ernie Camacho was signed as a free agent by the Cardinals.
August 29, 1990: Willie McGee was traded by the Cardinals to the Oakland Athletics for Félix José, Stan Royer, and Daryl Green (minors). However, McGee would win the NL batting title (he had enough plate appearances to qualify for it despite this trade)