Swiss media said the former pastor and psychologist died in mid-September but his family only announced his death on Thursday.
Sigg was one of 69 people who came together in 1982 to found Exit, becoming the director of the organization's Swiss German arm.
A member organization with currently 105,000 members in the German-speaking part of Switzerland alone, Exit helps those with incurable illnesses to end their lives.
Under Sigg's direction more than 500 people used its services.
His work earned him the nickname ‘angel of death' and he frequently faced resistance from protestors, said news agency ATS. In 1986 he was stripped of his post as pastor in Granges, in the canton of Solothurn, because of his work. However in 2012 he was recognized with a bravery award.
Suicide assistance is legal in Switzerland as long as the assistant does not benefit financially from the person's death, therefore all ‘end-of-life' workers at Exit are unpaid volunteers.
Exit only offers its services to members, who must be Swiss or have permanent residency in Switzerland.
A second Swiss organization, Dignitas, also provides assisted suicide services to non-Swiss who live outside the country.