The Montreal Expos selected Raines in the fifth round of the 1977 Major League Baseball draft.[10] After debuting with six games as a pinch runner in 1979, he played briefly as a second baseman for the Expos in 1980 but soon switched to playing the outfield, and rapidly became a fan favorite due to his aggressiveness on the basepaths. In his strike-interrupted 1981 rookie season, he batted .304 and set a then Major League Baseball rookie record with 71 stolen bases, breaking the previous mark of 56 steals set by Gene Richards in 1977. Raines was caught stealing for the first time in 1981, after having begun his career with a then major league record 27 consecutive successful stolen bases. Raines was the runner-up for the National League’s Rookie of the Year Award in 1981, which was won by Los Angeles Dodgers pitcher Fernando Valenzuela.
Raines’ performance dipped in 1982, as he hit .277 with a .353 on-base percentage. At the end of the season, Raines entered treatment for substance abuse, having spent an estimated $40,000 that year on cocaine. To avoid leaving the drug in his locker, Raines carried it in his hip pocket, and slid headfirst when running the bases. He used cocaine before games, in his car, after games, and on some occasions between innings in the clubhouse. Raines would later testify at the Pittsburgh drug trials in September 1985.
In 1983, Raines stole a career high of 90 bases, the second-highest total in franchise history, and scored 133 runs, a franchise record. He was named Expos Player of the Year in 1983, 1985, and 1986. In each season from 1981 to 1986, Raines stole at least 70 bases. He had a career-high .334 batting average in 1986, winning the National League Batting Championship. Raines maintained a consistently high on-base percentage during this period and a rising slugging percentage, reaching a career peak of .429 in 1987. Although he never won a Gold Glove Award, Raines was an excellent defensive player who led the National League with 21 assists in 1983 and, with 4 double plays, tied for the league lead in double plays by an outfielder in 1985.
