The team 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 in 1889, but re-joined in 1890 to replace the last-place Brooklyn Gladiators club which had dropped out during the season. After the Association folded, the Orioles joined the National League in 1892.
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 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 (though not John McGraw or Wilbert Robinson) were moved across to the Brooklyn Dodgers of the National League by the joint ownership of the clubs.
Following a fourth-place finish in 1899, the National League eliminated four teams from the circuit, the Orioles among them. First-year player/manager John McGraw followed through on his threats to abandon the NL and form a club in the rival American League, doing so beginning in 1901. (Those newly-formed Orioles only stayed in Baltimore for two seasons before moving to New York and becoming the Highlanders.)
A high-minor league franchise in the Eastern League filled the void left by the Orioles in 1903, including local product and future baseball icon Babe Ruth, but top-level professional baseball would not return to Baltimore until the St. Louis Browns relocated to the city in 1954.
The Orioles played briefly at the old Oriole Park, in Harwood at 29th and Barclay Streets, from 1890 to 1891. (The 1901 AL Orioles-turned-Highlanders would play at the site a decade later.) During the 1891 season, the Orioles moved a few blocks away to Union Park on 25th Street, where they would play until they were removed from the NL after the 1899 season.
The original Orioles were one of the most storied teams in the history of the game. Managed by Ned Hanlon, they won NL pennants in 1894, 1895 and 1896, and sported some of the most colorful players in history including John McGraw, Wee Willie Keeler, Hughie Jennings, Joe Kelley, Wilbert Robinson, and Dan Brouthers.
They were rough characters who practically invented "scientific" baseball, the form of baseball played before the home run became the norm in the 1920s. Like the style known today as "small ball", the Orioles featured tight pitching, hit and run tactics, stolen bases, and precise bunting. One such play, where the batter deliberately strikes the pitched ball downward onto the infield surface with sufficient force such that the ball rebounds skyward, allowing the batter to reach first base safely before the opposing team can field the ball, remains known as a Baltimore Chop.