The founder of right-to-die organisation DignitySA, Sean Davison, is hoping to raise around R2.8m for his defence against two premeditated murder charges.
Davison, in his late 50s, was arrested at his home in Pinelands in September for the 2013 death of his friend Anrich Burger, who became a quadriplegic after a car crash.
Two months later, it emerged that he faced a second murder charge in connection with the death of Justin Varian - who had motor neuron disease - on July 25, 2015.
He maintains that he has not committed any offence.
"Having recently been charged with premeditated murder, I am now facing the legal fight of my life," he said on his fundraising campaign page.
The page has raised about $500 (around R7 000) of its $200 000 (around R2.8m) goal.
"Despite my legal team generously donating much of their time - the costs of this legal battle are likely to be enormous and, as such, I humbly seek financial support for this legal battle on behalf of my family and myself."
Davison is president of The World Federation of Right to Die Societies, which has launched its own fundraising campaign.
A trust account with his attorneys already received around R400 000 in donations.
He thanked everyone for their support.
"The time since my arrest has been the most difficult in my life, and without this support the anguish would have been much greater. The journey ahead will be a long and difficult one and my family and I take strength from your support and generosity."