| Competition: | Primeira Liga |
| Season: | 2004–05 |
| Dates: | 28 August 2004 – 22 May 2005 |
| Winners: | Benfica 31st title |
| Relegated: | Moreirense Estoril Beira-Mar |
| Continentalcup1: | Champions League |
| Continentalcup1 Qualifiers: | Benfica Porto Sporting CP |
| Continentalcup2: | UEFA Cup |
| Continentalcup2 Qualifiers: | Braga Vitória de Guimarães Vitória de Setúbal |
| Matches: | 306 |
| Total Goals: | 711 |
| League Topscorer: | Liédson (25 goals) |
| Biggest Home Win: | (13 November 2004) |
| Biggest Away Win: | 0–4 (3 times) |
| Highest Scoring: | Sporting CP 6–1 Boavista (13 November 2004) |
| Prevseason: | 2003–04 |
| Nextseason: | 2005–06 |
The 2004–05 Primeira Liga was the 71st edition of top flight of Portuguese football. It started on 28 August 2004 with a match between Belenenses and Marítimo, and ended on 22 May 2005.
Benfica won their 31st league title, with 65 points, three points ahead of the defending champions Porto. The league was contested by 18 clubs, and was considered one of the most competitive seasons in recent years.
The first goal of the season was scored by Belenenses centre-back Rolando. The first red card of the season was given to Vitória de Setúbal's Bruno Ribeiro, and the first yellow was given to Belenenses' Juninho Petrolina in the opening match of the season. Benfica and Porto were both qualified for the 2005–06 UEFA Champions League group stage, and Sporting CP qualified for the UEFA Champions League qualifying round. At the bottom of the table, Moreirense, Estoril and Beira-Mar were relegated to the Liga de Honra. Liédson was the top scorer with 25 goals.
Alverca, Paços de Ferreira, and Estrela da Amadora were consigned to the Liga de Honra following their final classification in 2003–04 season.
The other three teams were replaced by Estoril, Vitória de Setúbal, and Penafiel from the Liga de Honra.
| Team | Outgoing manage | Manner | Date of vacancy | Incoming manager | Date of appointment |
|---|---|---|---|---|---|
| Porto |  Luigi Delneri | Sacked | 7 August 2004[1] |  Víctor Fernández | 11 August 2004[2] |
| Víctor Fernández | Sacked | 1 February 2005[3] |  José Couceiro | 1 February 2005[4] | |
| Boavista | Jaime Pacheco | Resigned | 1 May 2005[5] | Pedro Barny | 1 May 2005 |
| Team | Outgoing manager | Replaced by |
|---|---|---|
| Marítimo | Manuel Cajuda | Mariano Barreto |
| Vitória de Setúbal | José Couceiro | José Rachão |
| Penafiel | Manuel Fernandes | Luís Castro |
| Nacional |  Casemiro Mior | João Carlos Pereira |
| Gil Vicente | Luís Campos | Ulisses Morais |
| Académica de Coimbra | João Carlos Pereira | Nelo Vingada |
| Moreirense | Vítor Oliveira | Jorge Jesus |
| Beira-Mar | Mick Wadsworth | Luís Campos |
| Luís Campos | Augusto Inácio |
| Rank | Scorer | Goals | Team |
|---|---|---|---|
| 1 | Liédson | 25 | Sporting CP |
| 2 | João Tomás | 15 | Braga |
| Simão | Benfica | ||
| 4 | Wesley | 14 | Penafiel |
| 5 |  Henry Antchouet | 12 | Belenenses |
| 6 | Benni McCarthy | 11 | Porto |
 Albert Meyong | Vitória de Setúbal | ||
| 8 | Zé Manel | 10 | Boavista |
| 9 | Pena | 9 | Maritimo |
| Roberto | Penafiel |
The Footballer of the Year award was won by the Portuguese Ricardo Quaresma of Porto.
The Portuguese Golden Shoe award was won by the Brazilian Liédson of Sporting CP, scoring 25 goals.