Since the 1970s, he has been known for his commitment to environmental restoration, such as the restoration of a limestone quarry wasteland in Mombasa, Kenya, into the nature park and wildlife sanctuary named Haller Park.
Haller is a recipient of a number of awards.
He was one of the first recipients of the prestigious Global 500 Roll of Honor by the United Nations for his 'outstanding environmental achievements.
He is a Trustee of the Haller Foundation, the Director of The Baobab Trust, and interim Chair of the Kenyan Wildlife Service Board of Trustees.