Born in Aix-les-bains, France, Soheil started racing motocross before switching to karts in 1987.
In 1992 he entered the Volant Elf scholarship series. Down to the last five from the 340 entrants, Ayari ended up in the runner up spot. Dissapointed to to win the Formula Renault drive, he turned to Formula Ford and the Volant Maxauto series which had as a prize a season with a top team in the French Formula Ford Championship in 1993. He won and entered the French series taking a number of good placings including a win at Montlhéry in the final round.
Tipped to do well in 1994 he does not dissapoint and takes the French Formual Ford title. He also entered the Formual Ford Festival at Brands Hatch. He finished secong in the seni final and was in second and on the tail of James Watt in the final when he was hit from behind by Guy Smith.
He moved to Formual 3 in 1995 and after good first season he took French Formula Three championship the following year as well as the Macau Formula Three GP in 1997. He drove in F3000 for Astromega during 1997 and though Ayari could be impetuous on occasion, he did take a spectacular win in Helsinki, passing Oliver Tichy with an outrageouse overtaking manouver. Apart from that however, he scored a mere two points. He had a test with the Williams F1 team at the end of the year. However despite putting in a very good performance he missed out on the chance to become their test driver for 1998.
He coninued in F3000 taking another win in 1998 driving for Durango at the A-1 Ring ahead of Montoya, before moving on to French Supertouring Cars in 2001 where he became champion in his second season.
He won the title agin in 2004 and in 2005. In 2004 he also drove for Pescarolo-Judd in the Le Mans Endurance Series.
In 2006 he drove in the Le Mans Series Championship in GT1 for the Team Oreca, winning the French Championship with 7 wins driving a Saleen S7-R.
He won the French GT Championship again in 2007 as well as winning the LMGT1 class at the le Mans 24 Hour race. At le Mans in 2008 he finished 8th.