| Bill Gallagher | |
| Position: | Outfielder/Pitcher |
| Bats: | Unknown |
| Throws: | Left |
| Birth Date: | Unknown |
| Birth Place: | Philadelphia, Pennsylvania |
| Debutleague: | MLB |
| Debutdate: | May 2 |
| Debutyear: | 1883 |
| Debutteam: | Baltimore Orioles |
| Finalleague: | MLB |
| Finaldate: | June 18 |
| Finalyear: | 1884 |
| Finalteam: | Philadelphia Keystones |
| Statleague: | MLB |
| Stat1label: | Batting average |
| Stat1value: | .138 |
| Stat2label: | Home runs |
| Stat2value: | 0 |
| Stat3label: | Runs scored |
| Stat3value: | 11 |
| Stat4label: | Win–loss record |
| Stat4value: | 1–7 |
| Stat5label: | Earned run average |
| Stat5value: | 4.70 |
| Teams: | |
William John Gallagher was a Major League Baseball outfielder and pitcher. He played in the American Association for the 1883 Baltimore Orioles, in the National League for the 1883 Philadelphia Quakers and in the Union Association for the 1884 Philadelphia Keystones.