The 1984 Portuguese Grand Prix was a Formula One motor race held at Estoril on 21 October 1984. It was the sixteenth and final race of the 1984 FIA Formula One World Championship.

Niki Lauda needed second place to secure the title, and gained it when Nigel Mansell spun out with 18 laps to go. As a result, he took the title by just half a point from team-mate Alain Prost. The point-scoring drivers won a total of 13 world championships between them, and the three drivers on the podium were all (at least) triple World Champions from different eras – Lauda, approaching the end of his long and distinguished F1 career, Prost, enjoying the best years of his career, and Ayrton Senna, still at the dawn of his.

After running a strong second behind Prost for most of the race, Mansell's spin on lap 52 was due to his front left brake failing. The Englishman later told that as it was his last race for Lotus before joining Williams in 1985, team boss Peter Warr (whom he had never got along with personally) had refused to give him the brakes he wanted for his Lotus 95T and that it was this that ultimately caused his retirement and handed Lauda the second place he needed to win the World Championship.