He was born in Brno, then in Czechoslovakia (now in the Czech Republic), where he trained as a landscape architect.
He established Terragram, a firm of landscape architects, in 1986, and was a co-founder of Room 4.1.3 in 1998, with Richard Weller, a professor at the University of Western Australia (now Professor and Chair of Landscape Architecture at the University of Pennsylvania).
Their landscaping schemes have won many design competitions and prizes.
Built projects include the Garden of Australian Dreams at the National Museum of Australia in Canberra, and it also worked on Fusionpolis in Singapore (jointly with Oculus).
Sitta won the state of Berlin's Peter Joseph Lenné Prize in 1981 and 1986, and won the President's Award of the Australian Institute of Landscape Architects in 2002.