| 1899-00 | Formed to replace the defunct Royal Artillery Portsmouth club, |
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| and elected straight into the first division of the Southern |
|
| League |
|
| Southern League runner-up |
| 1900-01 | Also joined Western League |
|
| Western League Champions |
| 1901-02 | Southern League Champions |
|
| Western League Champions (2nd time) |
| 1902-03 | Western League Champions (3rd time) |
| 1906-07 | Southern League runner-up |
| 1907-08 | Western League Division 1A runner-up |
| 1911 | Relegated to Division Two |
| 1911-12 | Southern League Division Two runner-up, missed title on goal av. |
| 1919-20 | Southern League Champions (2nd time) (on goal average) |
| 1920-21 | Founder member of Division Three South |
| 1923-24 | Division Three South Champions |
|
| Promoted to Division Two |
| 1926-27 | Football League Division Two runner-up (on goal average) |
|
| Promoted to Division One |
| 1928-29 | F.A. Cup runner-up |
| 1933-34 | F.A. Cup runner-up |
| 1938-39 | F.A. Cup Winners |
| 1939-40 | Football League programme abandoned due to outbreak of war |
| 1948-49 | Football League Champions |
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| F.A. Cup semi-finalists |
| 1949-50 | Football League Champions (2nd time) on goal average |
| 1958 | Escaped relegation to Division Two on goal average |
| 1959 | Relegated to Division Two |
| 1961 | Relegated to Division Three |
| 1961-62 | Football League Division Three Champions |
|
| Promoted to Division Two |
| 1976 | Relegated to Division Three |
| 1978 | Relegated to Division Four |
| 1979-80 | Promoted to Division Three (on goal difference) |
| 1982-83 | Football League Division Three Champions |
|
| Promoted to Division Two |
| 1984-85 | Missed promotion by goal difference |
| 1986-87 | Football League Division Two runner-up |
|
| Promoted to Division One |
| 1987 | Relegated to Division Two |
| 1991-92 | F.A. Cup semi-finalists |
| 1992-93 | Division Two re-designated Division One on formation of F A |
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| Premiership |
|
| Missed runner-up spot and automatic promotion place on goals |
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| scored, and not promoted after play-offs (SF Leicester City 1 |
|
| Portsmouth 0, Portsmouth 2 Leicester City 2 - Agg 2-3) |
| 1996 | Escaped relegation on goals scored |
| 1999 | Escaped relegation on goals scored |
| 2002-03 | Football League Champions (3rd time) |
|
| Promoted to F A Premiership |
