The franchise that would become the Orioles was founded in 1894 as a minor league team based in Milwaukee, Wis., called the Brewers. The Brewers became a major league team in 1901 when their league—the renamed American League—was elevated to major league status. They moved to St. Louis, Mo., in 1902 and became known as the Browns. The St. Louis Browns featured Hall of Famers George Sisler (Sisler, George) and Bobby Wallace, but the team was not a success, reaching the World Series only once in their 52 years in St. Louis (1944, when they lost to their crosstown rivals, the St. Louis Cardinals). Possibly the most notable moment in Browns' history took place in a game against the Detroit Tigers on Aug. 19, 1951, when publicity-savvy owner Bill Veeck (Veeck, Bill) sent to the plate 3-foot 7-inch (1.09-metre) Eddie Gaedel, who walked on four straight pitches.

In 1992 the Orioles started playing their home games in Oriole Park at Camden Yards. The baseball-only facility began a trend in the major leagues away from suburban multipurpose stadiums and toward ballparks located near the heart of a city. These new stadiums were meant to be evocative of the idiosyncratic ballparks of baseball's early years, and they contributed greatly to the record attendance at baseball games by the turn of the 21st century. Due in part to the increased revenue brought to the team by the popularity of Camden Yards, the Orioles briefly returned to contention in the mid-1990s, but following a series of questionable personnel changes the team fell from baseball's top ranks by 1998. In 1999 the Orioles traveled to Cuba, where they became the first American baseball team in 40 years to play a game there, and defeated the Cuban National team.