The 1886 St. Louis Browns season was the team's fifth season in St. Louis, Missouri, and the fifth season in the American Association. The Browns went 93–46 during the season and finished first in the American Association, winning their second pennant in a row. In the World Series the Browns played the National League champion Chicago White Stockings, winning the series 4 games to 2. This was the only win by the AA in seven postseason contests with the NL from 1884 to 1890.

The St. Louis Cardinals, a professional baseball franchise based in St. Louis, Missouri, compete in the National League (NL) of Major League Baseball (MLB). As the game of baseball garnered interest in the United States in the 19th century, professional baseball in St. Louis became rooted chiefly in one disestablished Major League club – named the Brown Stockings, the same as the Cardinals' earliest name – which is loosely connected, but does not fall within the scope of, today's Cardinals. The Brown Stockings became St. Louis' first fully professional baseball club when they gained accession in the National Association (NA) in 1875. However, the NA folded after that season. That winter, with five other former NA teams, St. Louis established a new, eight-team league called the National League (NL) and began play the next season. Despite early success, Brown Stocking players were found to be connected to game fixing scandals, which forced bankruptcy and the club's expulsion from the NL. This scandal also abrogated their professional status but some members maintained play as a semi-professional team, primarily operated by outfielder Ned Cuthbert, until 1881.