The Hartford Dark Blues were a member of the National Association of Professional Base Ball Players in 1874 and 1875 and the National League in 1876 and 1877. In 1877 the team played in Brooklyn, New York as the Brooklyn Hartfords.
Playing at the Hartford Ball Club Grounds, in 1876 they joined the National League as a charter member. The team's owner, Morgan G. Bulkeley, was also the first president of the National League. Managed by their third baseman, Bob Ferguson, the Dark Blues went on to finish third in 1876 with a record of 47–21.
The team's strong suit was pitching, with both Tommy Bond and future Hall of Famer Candy Cummings finishing with an earned run average under 2. The pitching staff recorded the most complete games (69) and allowed the lowest number of home runs throughout the 70-game 1876 campaign (the Philadelphia Athletics also accomplished this feat that season). The team's best hitter was right fielder Dick Higham, who led the team in most offensive categories.
The team left Hartford and moved to Brooklyn, New York for the 1877 season to become the Brooklyn Hartfords. Managed again by Ferguson, the team finished in third again, with a record of 31–27. With Bond, Cummings and Higham all having left the team, the team's best player this year was undoubtedly right fielder John Cassidy, who batted .378 and also led the team in many other categories.
The team disbanded after the 1877 season and was replaced in the league with the Providence Grays. Author Mark Twain was a fan of the team.