The Netherlands international, 22, has signed a four-year contract with the Portuguese club.
Martins Indi revealed on Monday that he had agreed to join another team, though he stopped short of naming them.
The versatile defender leaves Feyenoord following a four-year spell with the Eredivisie side.
Martins Indi made his senior debut back in 2010 after coming through the club's youth system.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | PSV EindhovenPSV | 12 | 11 | 0 | 1 | 40 | 9 | 31 | 33 |
| 2 | FC UtrechtUtrecht | 11 | 9 | 1 | 1 | 20 | 11 | 9 | 28 |
| 3 | Ajax | 11 | 8 | 2 | 1 | 25 | 11 | 14 | 26 |
| 4 | Feyenoord | 12 | 7 | 4 | 1 | 28 | 13 | 15 | 25 |
| 5 | FC Twente | 12 | 6 | 4 | 2 | 24 | 11 | 13 | 22 |
| 6 | AZ AlkmaarAZ | 12 | 5 | 2 | 5 | 23 | 14 | 9 | 17 |
| 7 | Fortuna SittardSittard | 12 | 5 | 2 | 5 | 13 | 16 | -3 | 17 |
| 8 | NECNijmegen | 12 | 5 | 1 | 6 | 19 | 10 | 9 | 16 |
| 9 | Willem II | 12 | 4 | 3 | 5 | 13 | 12 | 1 | 15 |
| 10 | Go Ahead Eagles | 12 | 4 | 3 | 5 | 15 | 20 | -5 | 15 |
| 11 | NAC BredaNAC Breda | 12 | 5 | 0 | 7 | 12 | 21 | -9 | 15 |
| 12 | Heerenveen | 12 | 4 | 2 | 6 | 13 | 23 | -10 | 14 |
| 13 | Groningen | 12 | 3 | 3 | 6 | 12 | 19 | -7 | 12 |
| 14 | PEC Zwolle | 12 | 3 | 3 | 6 | 14 | 22 | -8 | 12 |
| 15 | Heracles | 12 | 3 | 3 | 6 | 12 | 23 | -11 | 12 |
| 16 | Sparta RotterdamSparta | 12 | 2 | 5 | 5 | 12 | 18 | -6 | 11 |
| 17 | Almere CityAlmere City | 12 | 1 | 3 | 8 | 6 | 27 | -21 | 6 |
| 18 | RKC WaalwijkRKC Waalwijk | 12 | 1 | 1 | 10 | 10 | 31 | -21 | 4 |
| > Eredivisie Full Table | |||||||||
