After the season, the Detroit Tigers bought his contract, and he made his major league debut the following season on April 18, 1914. In July 1914, Kavanagh forgot to set his alarm and missed part of a game; backup infielder Billy Purtell's poor play led to the Tigers losing the game as a result. Kavanagh finished the 1914 season with a .248 batting average and 16 stolen bases in 128 games. In 1915, he had his best year in professional baseball. In 113 games, 44 at first base and 42 at second base, he had a .295 batting average and 13 triples. In 1916, Kavanagh struggled; his average fell to .141 in 58 games for the Tigers.