Hanlon had a longer and more illustrious career as a manager than as a player. Though never much of a hitter, he was the centerfielder for the National League Detroit club from 1881 through 1888. In 1889 he went to the Pirates, and by season’s end he was their manager. In 1890 he was one of the discontented players that formed the Players’ League, but when the league folded he was taken back by the Pirates. He lasted for 78 games as their manager, and took over the Baltimore Orioles in 1892. There he remained through 1898.
In Baltimore, Hanlon put together one of the most famous 19th-century teams. They finished first in 1894-96, becoming known for their temperament, aggressive tactics, and heads-up play. Hanlon was partially responsible for the widespread use of the hit-and-run, fielders covering each other on plays, and the full-time use of a groundskeeper. His cunning rubbed off on such future managers as John McGraw, Hughie Jennings, Wilbert Robinson, Kid Gleason, and Miller Huggins. He was such an autocrat that Orioles owner Harry Vonderhorst wore a button that said “Ask Hanlon.”
With owners having a hand in more than one club, it was decided in 1899 that Hanlon and his top players go to the Brooklyn Superbas (later known as the Dodgers), which had more drawing power; Baltimore folded after the season. In Brooklyn, Hanlon led his team to two consecutive pennants in 1899 and 1900. Let go after a last-place finish in 1905, he was picked up by Cincinnati, which placed sixth in Hanlon’s two final years as a ML manager.