Speaker was born on April 4, 1888, in Hubbard, Texas, to Archie and Nancy Poer Speaker. As a youth, Speaker broke his arm after he fell from a horse; the injury forced him to become left-handed. In 1905, Speaker played a year of college baseball for Fort Worth Polytechnic Institute. Newspaper reports have held that Speaker suffered a football injury and nearly had his arm amputated around this time; biographer Timothy Gay characterizes this as "a story that the macho Speaker never disspelled [sic]."

Speaker became the regular starting center fielder for Boston in 1909 and light-hitting Denny Sullivan was sold to the Cleveland Naps. Speaker hit .309 in 143 games as the team finished third in the pennant race. Defensively, Speaker was involved in 12 double plays, leading the league's outfielders, and had a .973 fielding percentage, third among outfielders. In 1910 the Red Sox signed left fielder Duffy Lewis. Speaker, Lewis and Harry Hooper formed Boston's "Million-Dollar Outfield", one of the finest outfield trios in baseball history. Speaker was the star of the Million-Dollar Outfield. He ran fast enough that he could stand very close to second base, effectively giving the team a fifth infielder, but he still caught the balls hit to center field. In 1910 and 1911, Boston finished fourth in the American League standings. Speaker's best season came in 1912. He played every game and led the American League (AL) in doubles (53) and home runs (10). He set career highs with 222 hits, 136 runs, 580 at-bats, and 52 stolen bases. Speaker's stolen base tally was a team record until Tommy Harper stole 54 bases in 1973. He batted .383 and his .567 slugging percentage was the highest of his dead-ball days. Speaker set a major league single-season record with three hitting streaks of twenty or more games (30, 23, and 22). He also became the first major leaguer to hit 50 doubles and steal 50 bases in the same season. In August, Speaker's mother unsuccessfully attempted to convince him to quit baseball and come home. In Fenway Park's first game, Speaker drove in the winning run in the 11th inning, giving Boston the 7-6 win. The 1912 Red Sox won the AL pennant, finishing 14 games ahead of the Washington Senators and 15 games ahead of the Philadelphia Athletics. In the 1912 World Series, Speaker led the Red Sox to their second World Series title by defeating John McGraw's New York Giants. After the second game was called on account of darkness and ended in a tie, the series went to eight games. The Red Sox won the final game after Fred Snodgrass dropped an easy fly ball and later failed to go after a Speaker pop foul. After the pop foul, Speaker tied the game with a single. The Red Sox won the game in the bottom of the tenth inning. He finished the series with a .300 batting average, nine hits and four runs scored. Speaker was named the AL Most Valuable Player (MVP) for 1912. Though he did not lead the league in any offensive categories in 1913, Speaker finished fourth in AL MVP voting. Speaker batted .338 and tied his career high of 12 double plays as an outfielder in 1914. He hit .322 in 1915. The Red Sox beat the Philadelphia Phillies in the 1915 World Series. The Red Sox were led by pitcher Babe Ruth, who was playing in his first full season. Ruth won 18 games and hit a team-high four home runs. Speaker got five hits, including a triple, in 17 at-bats during the series. He scored twice but did not drive in any runs.

What else did he accomplish?
He also became the first major leaguer to hit 50 doubles and steal 50 bases in the same season.