They did not meet on track in the juniors. Prost won the French senior karting championship and the 1979 European F3 title; Senna won the South American karting championship before taking the 1983 British F3 title. Both skipped directly from F3 to F1.
They first crossed off the track. McLaren needed a partner for Niki Lauda in 1984 and granted Senna a test for late October 1983. Then Renault unexpectedly fired Prost, the 1983 runner-up; Prost beat Senna to McLaren by a week. After Brabham's Piquet and sponsor Parmalat vetoed him, Senna joined Toleman for its £100,000 release clause.
They finally met in equal machinery at the May 1984 Nürburgring Race of Champions, an exhibition Mercedes-Benz had arranged to showcase the new 190 E 2.3-16. Both wanted to win; they qualified first and third. Senna punted Prost off early and held off Lauda for the victory.
Ahead of 1988, Honda made clear that any team that wanted its engines would have to sign Piquet or Senna. Senna told Ron Dennis that if McLaren signed him he would steer Honda their way; Williams declined a Piquet–Nakajima pairing, and McLaren got both. Prost backed Senna over Piquet when Dennis asked — a decision he would come to regret. As a concession, Honda let McLaren announce the two would compete on equal terms.
What followed was one of the most dominant seasons in F1 history: 15 wins from 16, the Constructors' title, a then-record 199 points. Senna took 8 wins and 13 poles, Prost 7 wins and 2 poles. Under a scoring system that rewarded Senna's wins over Prost's consistency, Senna won the Drivers' title.
They raced cleanly until it became clear they were only racing each other. The flashpoint was the Portuguese Grand Prix, with Senna leading by three points and four races left. On lap two Prost moved to overtake; Senna swerved towards him at around 280 km/h, nearly pinning him into the pit wall. Prost held his line, came so close to the wall he nearly hit March's Ian Phillips, and took the corner. He won; Senna finished a distant sixth. "If that's how he wants to win the championship, I'm not interested," Prost said. "I don't want any part of it." Senna later apologised.
By year's end Prost suspected Honda was favouring Senna and met Honda's Nobuhiko Kawamoto in Geneva that November. In Prost's account, Kawamoto confirmed it — Honda's engineers liked Senna's panache and "samurai"-like driving — but promised parity for 1989. Kawamoto was promoted out of the role soon after.
McLaren-Honda comfortably won the 1989 Constructors' title; within the team, the relationship deteriorated.
The first rupture came at Imola. The drivers had agreed that whoever won the start would not be challenged into the first turn. Senna led; Prost honoured the deal. Then a Berger crash forced a red flag. Prost won the restart, only for Senna to pass him almost immediately on the basis that the agreement did not cover restarts. Prost told a French journalist, who published the story; Senna denied any pact had existed, but eyewitness John Hogan backed Prost. Dennis forced Senna to apologise; Senna was furious that Prost had gone public.
Engine-parity complaints continued. After Mexico, Prost publicly attacked McLaren and Honda over straight-line speed, noting Senna had out-powered him even with a tow or fresh tyres. Honda sent McLaren an engine crate marked "Special — For Ayrton." Honda's Osamu Goto told reporters that Senna's foot-tapping accelerator style suited the engine's mid-range better than Prost's smoother technique. Dennis began allocating engines randomly.
Ahead of Monza, Prost announced he would leave for Ferrari in 1990. He won the race after Senna's engine blew, then dropped his trophy into the Ferrari tifosi rather than handing it back as McLaren policy required. Senna pushed Dennis to fire him; McLaren instead made Prost finish the year in exchange for a written apology.
He went into Suzuka 16 points ahead. On lap 46, leading, Prost squeezed Senna at the slow Casio chicane as Senna lunged for the inside, and the two collided. Prost climbed out believing he had the title. Senna got a marshal bump-start, pitted for a new front wing, and won — only to be disqualified for re-entering via the escape road and cutting the chicane. Balestre dismissed the appeal, fined Senna $100,000 for "dangerous driving", and imposed a suspended six-month ban. Senna threatened to retire. Dennis told him: "If you stop, they've won."
The 1990 Ferrari 641 was the first car to seriously threaten McLaren-Honda. After a back-and-forth season, a Jerez pit-stop swing left Prost mirroring Senna's 1989 position: he needed both remaining races; Senna needed him to crash out only once.
Suzuka decided it again. This time Senna drove into Prost at the first turn of the first lap, ending both races. Prost's verdict: Senna "tries to represent himself to the world as a man he is not. He has no value." Honda telemetry showed Senna had kept the throttle open all the way through Turn 1, and Dennis privately reached the same conclusion, but the video was not conclusive and Senna was not penalised.
Senna admitted the crash had been deliberate only after Max Mosley replaced Balestre at FISA in October 1991. He gave three reasons: revenge for Prost's "unforgiveable" 1989 conduct; his belief that Balestre had favoured his countryman for years; and Balestre's refusal in 1990 to grant him, as polesitter, the cleaner side of the grid, even though Prost had used that side in 1989. Mosley felt the act would normally have warranted disqualification, but sympathised over 1989, which he called "absolutely outrageous", and accepted Senna's statement that "at no time did I deliberately collide with Alain."
Vindication of a kind came at the 1990 Japanese Grand Prix drivers' briefing, when Piquet criticised the 1989 ruling, arguing it was dangerous to require a driver who had gone off to turn back into oncoming traffic. Many drivers voiced support; Senna got up and walked out. He disavowed his earlier conciliatory statement once Balestre lost control of FISA in late 1991.
After 1990 the rivalry was no longer primarily fuelled by on-track conflict; the two would never again seriously contest a championship at the same time. Senna took his third and final title in 1991, leading McLaren-Honda with Berger. Prost, in an uncompetitive Ferrari 642, posted his first winless season since his rookie year and was fired after comparing the car to a "truck"; Ferrari paid him to sit out 1992. The one 1991 flashpoint came at Hockenheim, where Senna ran Prost off; FISA ordered them to sit down and cool tensions.
In 1993 Prost returned with Williams-Renault and won his fourth title in what he called an "absolutely unbelievable" FW15C, "a good second a lap, minimum" faster than the rest of the grid. He outqualified Senna 15–1 and took 13 poles in 16 races. Senna, in a customer Ford-Cosworth McLaren with around 60 fewer horsepower, finished a relatively distant second — "relatively" because his win at a wet Donington Park, after overtaking four cars on the opening lap, left Prost third after seven pit stops, the most in F1 history. In the press conference Senna offered, with audible mockery, to swap cars.
Before the season Prost had negotiated a clause preventing Senna from joining Williams. On learning of it, Senna called him "a coward" who "must be prepared to race anybody, at any condition, at equal terms." By year's end Renault Sport president Patrick Faure was pressing for Senna in 1994; Prost, unwilling to be a teammate again, retired instead.
Once they were no longer competitors, they began mending the relationship. At Prost's last Grand Prix, the 1993 Australian Grand Prix at Adelaide, Senna pulled him onto the top step of the podium for an embrace. After Prost's retirement they spoke once or twice a week, mostly about driver safety and the legality of Benetton's 1994 car. On the last day of his life, Senna ate breakfast with Prost — by then a pundit for TF1 — and filmed an in-car lap of Imola for Prost's channel, telling the cameras: "A special hello to my…to our dear friend, Alain. We all miss you Alain." Prost said he was surprised and touched; they had not been particularly close at the end, but "in time we might have become friends."
Senna was killed when his Williams hit the barrier at the Tamburello corner during the 1994 San Marino Grand Prix. Prost said a part of himself had died with him. Senna had told a close friend that after Prost retired he realised how much of his motivation had come from fighting him. Though the obvious candidate to replace him at Williams, Prost said that out of respect he would not race in F1 again. He was, by his account, the one driver invited by the Senna family to visit their home after the death.
Prost was a pallbearer at the funeral. He had been unsure the Brazilian public would accept his presence; Jean-Luc Lagardère, whose wife was Brazilian, told him it would. Out of consideration for the rivalry, Senna's press officer arranged that Prost — and Jackie Stewart, who had angered Senna by criticising him after the 1990 Japanese Grand Prix — would not stand in the front row. Piquet did not attend; Bernie Ecclestone was explicitly banned by the Senna family.
At the close of their careers Prost held the records for most wins (51), fastest laps (41) and podium finishes (106); Senna held the record for most pole positions (65). Prost won four Drivers' titles, three at McLaren and one at Williams; Senna won three, all at McLaren. A 2022 meta-analysis found that more mathematical approaches tend to favour Prost while critic rankings and driver and fan polls show "a clear tendency towards Senna."
The rivalry has since been refracted through screen as much as statistics. Asif Kapadia's 2010 documentary Senna sparked a new wave of interest; its makers acknowledged casting Prost as antagonist for narrative reasons, and writer Manish Pandey conceded they had erred by leaving out moments — Senna's Estoril 1988 block on Prost, Prost's Imola 1989 accusations — that complicated the picture. A 2024 Netflix miniseries made with the family's involvement, and a 2024 Canal+ docuseries on Prost, drew similar criticism. Prost himself observed that since his retirement, his career and life had been "reduced" to the rivalry.