This is a list of Portuguese prime ministers by time in office.
Of the 90 prime ministers, 8 have served more than eight years, while 56 have served less than one year.
António Oliveira Salazar served as prime minister for more than 36 years, whereas Francisco Fernandes Costa didn't even serve as prime minister because he refused to take the oath of office.
| Rank by length of terms | Prime Minister | Length by time served | Cabinets | Party |
|---|---|---|---|---|
| 1 | 36 years, 82 days | 3 | National Union | |
| 2 | 11 years, 26 days | 3 | Regenerator | |
| 3 | 9 years, 356 days | 3 | Social Democratic | |
| 4 | 8 years, 288 days | 3 | Progressist | |
| 5 | 8 years, 203 days | 4 | Regenerator | |
| 6 | 8 years, 131 days | 3 | Regenerator | |
| 7 | 8 years, 128 days | 3 | Socialist | |
| 8 | 8 years, 123 days | 3 | Historic | |
| 9 | 6 years, 160 days | 2 | Socialist | |
| 10 | 6 years, 101 days | 2 | Socialist | |
| 11 | 5 years, 290 days | 4 | Regenerator | |
| 12 | 5 years, 210 days | 1 | National Union | |
| 13 | 4 years, 187 days | 2 | Socialist | |
| 14 | 4 years, 158 days | 2 | Social Democratic | |
| 15 | 3 years, 310 days | 5 | Reformist | |
| 16 | 3 years, 64 days | 3 | Regenerator | |
| 17 | 2 years, 166 days | 1 | National Union | |
| 18 | 2 years, 151 days | 1 | Social Democratic | |
| 19 | 2 years, 132 days | 4 | Democratic | |
| 20 | 2 years, 119 days | 3 | Reformist | |
| 21 | 2 years, 102 days | 1 | Social Democratic | |
| 22 | 1 year, 329 days | 3 | Democratic | |
| 23 | 1 year, 312 days | 2 | Chartist | |
| 24 | 1 year, 297 days | 1 | Progressist | |
| 25 | 1 year, 284 days | 1 | Independent | |
| 26 | 1 year, 261 days | 1 | Liberal Regenerator | |
| 27 | 1 year, 195 days | 1 | Septemberist | |
| 28 | 1 year, 95 days | 1 | Independent | |
| 29 | 1 year, 81 days | 1 | Independent | |
| 30 | 1 year, 63 days | 1 | Independent | |
| 31 | 1 year, 40 days | 1 | Evolutionist Party | |
| 32 | 1 year, 35 days | 1 | Independent | |
| 33 | 1 year, 23 days | 2 | Democratic | |
| 34 | 1 year, 9 days | 1 | National Republican | |
| 35 | 363 days | 3 | Chartist | |
| 36 | 336 days | 1 | Social Democratic | |
| 37 | 326 days | 1 | Independent | |
| 38 | 323 days | 1 | Republican | |
| 39 | 278 days | 3 | Democratic | |
| 278 days | 1 | Independent | ||
| 40 | 270 days | 1 | Regenerator | |
| 41 | 252 days | 1 | Social Democratic | |
| 42 | 238 days | 1 | Social Democratic | |
| 43 | 236 days | 1 | Regenerator | |
| 44 | 222 days | 1 | Septemberist | |
| 222 days | 1 | Independent | ||
| 45 | 216 days | 1 | Republican | |
| 46 | 212 days | 1 | Nationalist Republican | |
| 47 | 207 days | 1 | Republican | |
| 48 | 205 days | 1 | Democratic | |
| 49 | 197 days | 1 | Independent | |
| 50 | 196 days | 1 | Democratic | |
| 51 | 186 days | 1 | Regenerator | |
| 52 | 174 days | 2 | Republican Liberal | |
| 53 | 155 days | 1 | Independent | |
| 54 | 154 days | 1 | Independent | |
| 55 | Luís Montenegro | (Incumbent) | 1 | Social Democratic |
| 56 | 138 days | 1 | Democratic | |
| 57 | 136 days | 1 | Democratic | |
| 58 | 106 days | 1 | Independent | |
| 106 days | 1 | Independent | ||
| 59 | 101 days | 1 | Regenerator | |
| 60 | 99 days | 1 | Republican Liberal | |
| 61 | 92 days | 1 | Democratic | |
| 62 | 90 days | 1 | Democratic | |
| 63 | 86 days | 1 | Independent | |
| 64 | 85 days | 1 | Democratic Leftwing Republican | |
| 65 | 72 days | 1 | Republican | |
| 66 | 63 days | 1 | Independent | |
| 67 | 62 days | 1 | Septemberist | |
| 62 days | 1 | Independent | ||
| 68 | 55 days | 1 | Septemberist | |
| 69 | 53 days | 1 | Democratic | |
| 70 | 47 days | 1 | Democratic | |
| 71 | 41 days | 1 | Independent | |
| 72 | 36 days | 1 | Democratic and Social Centre | |
| 73 | 35 days | 1 | National Republican | |
| 74 | 33 days | 1 | Independent | |
| 33 days | 1 | Nationalist Republican | ||
| 75 | 30 days | 1 | Independent | |
| 76 | 23 days | 1 | Chamorro | |
| 77 | National Salvation Junta | 21 days | 1 | Independent |
| 78 | 20 days | 1 | Democratic | |
| 20 days | 1 | Independent | ||
| 20 days | 1 | Independent | ||
| 79 | 17 days | 1 | Independent | |
| 80 | 9 days | 1 | National Republican | |
| 81 | 1 day | 1 | Independent | |
| Constitutional Junta | 1 day | 1 | Independent | |
| 82 | less than a day | – | Republican Liberal | |
| Rank by length of terms | Party | Length by time served | Prime ministers | |
|---|---|---|---|---|
| 1 | 44 years, 93 days | 3 | ||
| 2 | 38 years, 176 days | 9 | ||
| 3 | 25 years, 211 days | 4 | ||
| 4 | Social Democratic | (Incumbent) | 8 | |
| 5 | 11 years, 307 days | 25 | ||
| 6 | 10 years, 220 days | 2 | ||
| 7 | 8 years, 279 days | 13 | ||
| 8 | 8 years, 123 days | 1 | ||
| 9 | 6 years, 64 days | 2 | ||
| 10 | 2 years, 310 days | 2 | ||
| 11 | 2 years, 169 days | 4 | ||
| 12 | 2 years, 88 days | 4 | ||
| 13 | 1 year, 261 days | 1 | ||
| 14 | 1 year, 40 days | 1 | ||
| 15 | 1 year, 53 days | 3 | ||
| 16 | 273 days | 3 | ||
| 17 | 245 days | 2 | ||
| 18 | 85 days | 1 | ||
| 19 | 36 days | 1 | ||
| 20 | Chamorro | 23 days | 1 |