Grant signed with the Cleveland Indians in 1954 as an amateur free agent and made his big league debut with the Indians in 1958. His best season in Cleveland was in 1961 when he had a won-loss record of 15-9 and a 3.86 earned run average. In June 1964, he was traded to the Minnesota Twins and had a record of 11-9 for the remainder of the season. In 1965 Grant had the best year of his career. He was 21-7 for the Twins, helping to lead the team to the 1965 World Series against the Los Angeles Dodgers. In 1965, Grant hosted a local Minneapolis variety television program, The Jim Grant Show, where he sang and danced. He finished 6th in voting for the 1965 American League MVP for leading the league in wins, won-loss percentage, and shutouts. He also started 39 games and had 14 complete games, 270 ⅓ innings pitched, 252 hits allowed, 34 home runs allowed, 107 runs allowed, 99 earned runs allowed, 61 walks, 142 strikeouts, 8 wild pitches, 1,095 batters faced, 2 intentional walks issued, and a 3.30 ERA. Grant's home run in the 6th game of the 1965 World Series was only the second by an American League pitcher during a World Series game. 1966 was Grant's last year as a full-time starting pitcher. He spent his next five seasons in baseball as a reliever and occasional starter for five different big league clubs. He and Zoilo Versalles were traded by the Twins to the Dodgers for John Roseboro, Ron Perranoski and Bob Miller on November 28, 1967. Grant was the starting pitcher for the Montreal Expos in their first ever game on April 8, 1969. He pitched 1.1 innings while allowing six hits and three runs, starting his season off with a 20.25 ERA, although the Expos would later win the game in an 11-10 shootout that had nine combined pitchers in the game. In 14 years, he had a 145-119 record in 571 games, while starting in 293 of them and throwing 89 complete games and finishing 160 of them, 18 shutouts, 53 saves, with 2,442 innings pitched on a 3.63 ERA. Grant's home run during Game 6 of the 1965 World Series was the only one he hit that season and one of only seven he hit in his entire career. As a hitter, Grant posted a.178 batting average with 80 runs, 6 home runs, 65 RBI and 37 bases on balls. Defensively, he recorded a.966 fielding percentage. After his playing career ended, Grant worked for the North American Softball League, one of three Men's Professional Softball Leagues active in the pro softball era. He later worked as a broadcaster and executive for the Indians, and also as a broadcaster for the Athletics. In recent years, Grant has dedicated himself to studying and promoting the history of blacks in baseball. On his official website, Grant pays tribute to the fifteen black pitchers who have won 20 games in a season. The "15 Black Aces" are: Vida Blue, Al Downing, Bob Gibson, Dwight Gooden, Grant, Ferguson Jenkins, Sam Jones, Don Newcombe, Mike Norris, David Price, J. R. Richard, CC Sabathia, Dave Stewart, Dontrelle Willis, and Earl Wilson. In 2007, Grant released The Black Aces, Baseball's Only African-American Twenty-Game Winners, featuring chapters on each of the black pitchers to have at least one twenty-win season, and also featuring Negro League players that Mudcat felt would have been twenty game winners if they were allowed to play. The book was featured at the Baseball Hall of Fame during Induction Weekend 2006. In February 2007 during an event to honor Black History Month, President George W. Bush honored Grant and fellow Aces, Ferguson Jenkins, Dontrelle Willis and Mike Norris, and the publication of the book, at the White House. On April 14, 2008, he threw out the ceremonial opening pitch at Progressive Field to commemorate the 50th anniversary of his major league debut. Grant was also awarded the key to the city to honor the occasion. Grant was inducted into the Baseball Reliquary's Shrine of the Eternals in 2012. He was awarded the honorary Doctor of Humane Letters from Whittier College in 2016.
