The 78-year-old was diagnosed with cancer in late July and is survived by his wife Judy and two daughters Sally and Pip.
Kiernan's foundation confirmed the sad news with the following statement.
"It is with deep sadness that we pay tribute to our beloved founder and Chairman Ian Kiernan AO, who passed away in October 2018."
"Ian believed that Clean Up belongs to the millions of volunteers who have taken to their streets, beaches, parks, bushland and waterways to remove the rubbish that is bothering them."
"More recently this has extended to the thousands who take actions such as saying NO to a plastic bag at the checkout, refusing a single use item, or who join us via our social media campaigns."
"One man's vision created Clean Up Australia, the nations largest community mobilisation effort which is now firmly embedded in Australian and global culture."
Kiernan was a celebrated environmentalist, whose efforts earned him Australian of the Year back in 1994 and the following year he was appointed an Officer of the Order of Australia.
Prime Minister Scott Morrison addressed the sad news, "His passion for our oceans, which started all of this for him, and Australia's coastal lifestyle, in particular, is something that I think struck a real chord with all Australians."
"The thing that I think Ian did more than anything else was tap us all on the shoulder and say, 'hey, we've got to take care of this — this is our responsibility to do this, it's not the government's, it's ours, as Australians'."
This article originally appeared on WHO.