| Pat Hartnett | |
| Position: | First baseman |
| Bats: | Right |
| Throws: | Unknown |
| Birth Date: | October 20, 1863 |
| Birth Place: | Boston, Massachusetts |
| Death Place: | Boston, Massachusetts |
| Debutleague: | MLB |
| Debutdate: | April 18 |
| Debutyear: | 1890 |
| Debutteam: | St. Louis Browns |
| Finalleague: | MLB |
| Finaldate: | May 15 |
| Finalyear: | 1890 |
| Finalteam: | St. Louis Browns |
| Statleague: | MLB |
| Stat1label: | Batting average |
| Stat1value: | .189 |
| Stat2label: | Runs |
| Stat2value: | 6 |
| Stat3label: | Runs batted in |
| Stat3value: | 4 |
| Teams: |
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Patrick J. Hartnett (October 20, 1863 – April 10, 1935) was a professional baseball player. Nicknamed "Happy", he played part of one season in Major League Baseball for the St. Louis Browns in 1890.