The longest Major League Baseball (MLB) game ever played in terms of innings was a 26-inning game between the Brooklyn Dodgers and the Boston Braves on May 1, 1920. This game ended in a 1-1 tie after 26 innings, making it the longest game by innings in MLB history. Both starting pitchers, Leon Cadore of Brooklyn and Joe Oeschger of Boston, pitched the entire 26 innings, a record considered unbreakable in modern baseball due to current pitching practices and rules.

In terms of time, the longest game in MLB history was played on May 8, 1984, between the Chicago White Sox and the Milwaukee Brewers. That game lasted 8 hours and 6 minutes, covering 25 innings before a winner was decided.

Thus, the longest MLB game ever by innings is the 26-inning 1920 Dodgers vs. Braves game, and the longest by time is the 25-inning game in 1984 between the White Sox and Brewers.