The 1927 major league baseball season began on April 12, 1927. The regular season ended on October 2, with the Pittsburgh Pirates and New York Yankees as the regular season champions of the National League and American League, respectively. The postseason began with Game 1 of the 24th World Series on October 5 and ended with Game 4 on October 8. The Yankees swept the Pirates in four games, capturing their second championship in franchise history, since their previous in . Going into the season, the defending World Series champions were the St. Louis Cardinals from the season.
The New York Yankees, whose lineup featured Babe Ruth and Lou Gehrig of the famed "Murderers' Row," dominated the American League with 110 wins. No no-hitters were thrown during the season.
This was the sixth of eight seasons that "League Awards", a precursor to the Major League Baseball Most Valuable Player Award (introduced in 1931), were issued.
The 1927 schedule consisted of 154 games for all teams in the American League and National League, each of which had eight teams. Each team was scheduled to play 22 games against the other seven teams of their respective league. This continued the format put in place since the season (except for ) and would be used until in the American League and in the National League.
Opening Day took place on April 12 with all but all but the Detroit Tigers and St. Louis Browns playing. The final day of the regular season was on October 2. The World Series took place between October 5 and October 8.
The 1927 season saw the following rule changes:
An asterisk (*) denotes the ballpark a team played the minority of their home games at
8 tie games 5 in AL, 3 in NL), which are not factored into winning percentage or games behind (and were often replayed again) occurred throughout the season.
The postseason began on October 5 and ended on October 8 with the New York Yankees sweeping the Pittsburgh Pirates in the 1927 World Series in four games.
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In November 1926, following the conclusion of the previous season, Chicago Cubs owner William Wrigley Jr. renamed Cubs Park to Wrigley Field.
During a Philadelphia Phillies home game against the St. Louis Cardinals at the Baker Bowl on May 14, parts of two sections of the lower deck extension along the right-field line collapsed due to rotted shoring timbers, triggered by an oversize gathering of people, who were seeking shelter from rain. While no one died during the collapse, one individual died of heart failure in the subsequent stampede that injured 50. The game was cut short in the 7th inning following the collapse. In a similar situation to a partial collapse in , the Phillies rented from the Philadelphia Athletics at Shibe Park while repairs were being made to the old structure. The Phillies played 12 home games at Shibe Park, from May 16 to May 28, before eventually returning to the Baker Bowl on June 24 after spending nearly a month on the road.