stylistic:style_transfer, quality:corruption
1983–1984: testing and debut season

In 1983, Senna tested for Formula One teams Williams, McLaren, Brabham, and Toleman. Peter Warr of Lotus, Ron Dennis of McLaren, and Bernie Ecclestone of Brabham made offers for testing in 1984 and presented long-term contracts that tied Senna to driving later on. During his test for Williams at the 3.149-km (1.957-mi) Donington Park circuit, Senna completed 40 laps and was quicker than the other drivers, including Williams's reigning World Champion Keke Rosberg. Neither Williams or McLaren had a vacancy for the 1984 season.

Both Williams boss Frank Williams and McLaren boss Ron Dennis observed that Senna insisted that he got to run their cars before anyone else (other than their regular drivers such as Rosberg) so that he would have the best chance of a good showing by having a fresh car. Peter Warr actually wanted to replace Nigel Mansell with Senna at Lotus, but their British-based title sponsor, Imperial Tobacco (John Player & Sons), wanted a British driver. Senna was determined to drive that season and certainly on his own terms. Senna's test for Brabham occurred at Circuit Paul Ricard in November 1983. Senna impressed the Brabham team and was linked to their second seat. The team's main sponsor, Italian dairy company Parmalat, wanted an Italian driver. Brabham's second car was eventually shared by brothers Teo and Corrado Fabi, while Piquet convinced Ecclestone to sign his friend Roberto Moreno as the test driver. Consequently, Senna joined Toleman, a relatively new team, using less competitive Pirelli tyres. Venezuelan Johnny Cecotto, a former Grand Prix motorcycle racing world champion, was his teammate.

In 1984, Senna hired Nuno Cobra to assess his physical condition due to his concern over his low weight. Senna made his debut at the Brazilian Grand Prix in Rio de Janeiro, where he qualified 17th but retired when the Hart 415T turbocharger failed on lap 8. He scored his first World Championship point when he finished 6th in his second race at the South African Grand Prix at Kyalami with severe cramp in his neck and shoulders, and replicated that result two weeks later at the Belgian Grand Prix. A combination of tyre issues and a fuel-pressure problem resulted in his failure to qualify for the San Marino Grand Prix, the only time this happened during his career. Toleman decided not to run both cars during Friday qualifying at Imola due to a dispute with tyre supplier Pirelli (Toleman were in the process of switching from Pirelli to Michelin). Senna then suffered a fuel-pressure problem in the wet Saturday session at Tosa (the furthest point on the circuit from the pits) and did not have enough time for it to be fixed to allow him to make the grid. Senna's best result of the season came at the Monaco Grand Prix, the first wet-weather race of the season. Qualifying 13th on the grid, he made steady progress in climbing through the field, passing Niki Lauda for second on lap 19. He quickly began to cut the gap to race leader Alain Prost. Before he could attack Prost, the race was stopped on lap 31 for safety reasons, as the rain had grown even heavier. At the time the race was stopped, Senna was catching Prost by about 4 seconds per lap (while the Tyrrell - Ford of Stefan Bellof was catching both at the same rate, although he was later disqualified due to weight restrictions broken by Tyrrell).

Senna was renowned throughout his career for his capacity to provide very specific technical details about the performance of his cars and track conditions long before the advent of telemetry; this skill led Pat Symonds, Senna's first Formula One race engineer, to regard the Dallas Grand Prix in the United States as the initial highlight of Senna's debut season, instead of Monaco. In an interview, Symonds recalled:

The car was reasonably competitive there, so we expected to have a good race, but Ayrton spun early in the race. He then found his way back through the field in a quite effective way and we were looking for a pretty good finish, but then he hit the wall, damaged the rear wheel and the driveshaft and retired, which was a real shame. The real significance of that was that when he came back to the pits he told me what happened and said "I'm sure that the wall moved!" And even though I've heard every excuse every driver has ever made, I certainly hadn't heard of that one! But Ayrton being Ayrton, with his incredible belief in himself, the absolute conviction, he then talked me into going with him after the race to have a look at the place where he had crashed. And he was absolutely right, which was the amazing thing! Dallas being a street circuit, the track was surrounded by concrete blocks and what had happened – we could see it from the tyre marks – was that someone had hit at the far end of the concrete block and that made it swivel slightly, so that the leading edge of the block was standing out by a few millimetres. And he was driving with such precision that those few millimetres were the difference between hitting the wall and not hitting the wall. While I had been, at first, annoyed that we had retired from the race through a driver error, when I saw what had happened, when I saw how he had been driving, that increased my respect for the guy by quite a lot.

That season, Senna took two more podium finishes—third at the British and Portuguese Grands Prix—and placed 9th in the Drivers' Championship with 13 points overall. He did not take part in the Italian Grand Prix after he was suspended by Toleman for being in breach of his contract by entering talks with Lotus for 1985 without informing the Toleman team first. Although Senna did have a £100,000 buyout clause in his contract, the team had to be informed before discussions with another team started. Senna became the first driver Lotus had signed not personally chosen by team founder Colin Chapman, who had died in 1982. At the end of the year, Senna had developed Bell's palsy, possibly from a virus. One side of his face had become completely paralysed; Sid Watkins gave Senna steroids to preserve the possibility of recovery.