The Nobel Peace Prize laureate and anti-apartheid campaigner said that he did “not wish to be kept alive at all costs”, writing in the Washington Post newspaper on his 85th birthday.
Mr Tutu came out in favour of assisted dying in 2014, without specifying if he personally wanted to have the choice.
He was hospitalised last month for surgery to treat recurring infections.
“I hope I am treated with compassion and allowed to pass on to the next phase of life’s journey in the manner of my choice,” Mr Tutu wrote.
“Regardless of what you might choose for yourself, why should you deny others the right to make this choice?
“For those suffering unbearably and coming to the end of their lives, merely knowing that an assisted death is open to them can provide immeasurable comfort.”
There is no specific legislation in South Africa governing assisted dying.
But in a landmark ruling in April 2015, a South African court granted a terminally ill man the right to die, prompting calls for a clarification of the laws in cases of assisted death.
The Anglican Church – of which Mr Tutu is a member – is staunchly against assisted dying.
This is not the first time Mr Tutu has come out against the church, however.
He is an outspoken supporter of gay rights, and has openly criticised conservative Christian attitudes to homosexuality. In 2013, he said would “refuse to go to a homophobic heaven” in favour of “the other place”.
At the time, he added: “I would not worship a God who is homophobic and that is how deeply I feel about this.”
Earlier this year, he blessed his daughter Mpho’s marriage with her female partner, despite South African Anglican law on marriage stating that “holy matrimony is the lifelong and exclusive union between one man and one woman”.
The then-Archbishop of Cape Town also controversially supported an amendment to make abortion more readily available in South Africa in the mid-90s, despite some personal reservations.