McNish was born on the 29th of December, 1969 in Dumfries, Scotland where he grew up. Like most racing drivers, his career began at an early age, 11, in karting. For the five years he was in karting, until 1986, he was fairly successful and moved up to the next stage in racing. Formula Ford. In 1988 he made his first major achievement, winning the Vauxhall Lotus Championship. As a result, he entered Formula Three. In his first season in British Formula Three he came second, winning five events. He won the Autosport National Driver of the year and was tipped as a future Formula One driver.
The next step for the 21 year old driver was the F1 feeder series, Formula 3000. Before the F3000 season started he landed a test drive at McLaren. He joined the DAMS team in F3000 with his teammate, Érik Comas. The first race of the season was at Donington Park. Comas won the race, but McNish retired. He fared better at Silverstone for the second round, getting pole and winning the race, but his teammate still lead the championship with a second place finish. The next three races were disappointing for McNish with a second place and a win in the middle of the season before a string of retirements left him in fourth at the end of the season, with Érik Comas, his teammate winning and moving up to F1 the next year.
He stayed as McLaren test driver and F3000 driver for the next 2 years. 1991 was a nightmare year for him in F3000 with 1992 not an awful lot better. He was dropped by the McLaren team and moved to Benetton to continue testing. By now, McNish was 24 and past the prime age for drivers to enter F1, however the Scot and his fans remained confident he would make it to F1. He devoted 1993 to his testing duties at Benetton and in 1994 he took part in only 1 F3000 race in which he retired. In 1995 he tried to get his Formula 3000 career back on track, in one last attempt to enter Formula One. He joined the Paul Stewart Racing team. Allan came third in the first race at Silverstone. He got pole during the second race at the Circuit de Catalunia but retired and then came second in France. That was the end of his good results and he finished seventh overall. He once again left F3000 but stayed on as Benetton Test Driver for 1996. When he didn't get a race seat at the end of the season, he gave up on his Formula One ambitions and left the Benetton team.
He moved his career to sports car racing and by 1998 had entered the Le Mans 24 race with Porche. He won the 1998 24 hours of Le Mans with fellow porche drivers Laurent Aïello and Stéphane Ortelli. In 1999, McNish joined the Toyota team for the 24 hour race with Thierry Boutsen and Ralf Kelleners but retired during the race. However, he was asked by Toyota to join their F1 Project. For the 2000 race he moved once again to Audi with the two drivers he won the 1998 race, Ortelli and Aiello. The team finished second. Toyota had been given permission to enter Formula One in 2002 and made their first F1 car, the TF101, for testing purposes in 2001. Allan McNish became their official test driver. In 2002, when Toyota became a Formula One team, McNish was given the role of Second Driver for the entire season.