The team (formally the "Baltimore Base Ball and Exhibition Company") was founded in 1882 as a charter member of the American Association, which was then a major league. After several years of mediocrity, the team dropped out of the league after the 1889 season, but re-joined in 1890 to replace the Brooklyn Gladiators when that last-place team dropped out during the season. The Orioles were one of four AA clubs merged into the National League in 1892 (formally as a 12-member "League Association"). The beginnings of what was to become a legendary team can be traced to June 1892, when Harry Von der Horst hired Ned Hanlon to manage the Orioles giving him stock in the team and full authority over baseball operations. Ned moved his growing family to a house that stood a block away from Union Park.
After two years finishing near the bottom of the league, the Orioles won three consecutive pennants with several future Hall of Famers under player/manager Ned Hanlon from 1894 to 1896. They followed up the title run with two consecutive second-place finishes. Accordingly, they participated in all four editions of the post-season Temple Cup series, winning the final two in 1896 and 1897.
After the team's 1898 second-place finish, Hanlon and most of the team's stars were moved to the Brooklyn Dodgers of the National League by the joint ownership of the clubs. Third baseman John McGraw and catcher Wilbert Robinson remained in Baltimore, with McGraw remaining as first-year player/manager. Following a fourth-place finish in 1899, the Orioles were one of four clubs eliminated by the National League. In the 8-team National League of 1900, McGraw and Robinson joined the St. Louis Cardinals.
One year later McGraw followed through on his threats to abandon the NL and form a club in the rival American League (being formed by new president Ban Johnson out of the former minor Western League), doing so beginning in 1901. (Those newly formed A.L. Orioles only stayed in Baltimore for two seasons before being moved to New York as "the price of peace" as agreement was established in 1903 between the older circuit and its new upstart rival allowing the "Americans" to have a representative also in the "Big Apple" as a sign of respectability. The old Oriole franchise under McGraw became known as the "New York Highlanders" or occasionally the "New York Americans", later becoming renamed in 1913 as the New York Yankees.)
A high-minor league franchise in the old Eastern League filled the void left by the Orioles in 1903, including local product and future baseball icon Babe Ruth and Lefty Grove, even winning an unbroken string of six straight titles, 1919–1925 in the "Triple A" (AAA) level of minor league baseball in the reorganized International League (after 1911); but top-level professional baseball would not return to Baltimore until the St. Louis Browns relocated to the City in 1954.