The incident took place during the Classic Touring Car Racing Club's Pre 93 & Pre 03 Touring Car race, when two drivers made contact along the start-finish straight during the opening laps.
One car was sent into the barrier on the outside of the circuit where it was launched into the air and collided with a marshal's post.
The race was immediately halted while emergency crews attended the scene, including the air ambulance while Kent Police confirmed they were called shortly before 3pm "following a collision involving a car and a person on foot".
Shortly after 9pm, BARC released a statement confirming one marshal had died in the incident.
"The British Automobile Racing Club is saddened to confirm that as a result of an accident that occurred during a race meeting at Brands Hatch circuit today (Saturday 31 July), a volunteer marshal tragically lost their life," read a statement.
"The rest of the day’s racing activity was cancelled.
"As with any major incident, the BARC is now working with the national governing body, Motorsport UK, and the local police.
"On behalf of everyone connected with the BARC, we are devastated by loss of one of the amazing volunteer marshal community who do so much to enable the sport to take place. Our thoughts and best wishes are with the family and friends of all those involved.
"It is anticipated that the event will resume on Sunday."
It is understood that the driver was taken to hospital suffering a broken leg.