Hans was born in Berlin in 1910. His mother was Western Australian and his father was a leading German barrister. He studied law in Berlin, Paris and Heidelberg but politics interrupted his studies. A social democrat, he was strongly opposed to Nazism and, after his father had warned him that his arrest was imminent, fled to Paris. After a brief stay there, he moved in 1937 to Western Australia to stay with relatives of his mother.
The relatives lived on a farm in an environment which was a far cry from the major European cities that had been his life until then. The memory of his first sighting of the broken down farm and the rabbit proof fence became a favourite story. Before the war, he tried his hand at many different occupations including farming and travelling picture shows before joining the army. He also married Jean in November 1942 beginning a marriage of 41 years. He was somewhat amused that her marriage to him meant that she had to report to police weekly as the spouse of an enemy alien while he, being in the army, was under no such restriction. After serving overseas he returned to Western Australia and in 1950 joined the staff of the West Australian where he eventually became Chief Librarian.
Hans was first recorded as playing bridge in Western Australia in 1939 and he was for more than thirty years one of the strongest bridge players in Western Australia and had victories in all the major state events during this career. He was in the winning Open Team in the 1961, 1964, 1969, 1971 and 1973 championships and usually in a place otherwise, frequently playing with Geoff Holman. He won the Men's Pairs in 1962 (with Charles Porter), 1972 (with Mike Hopper) and with his son Nigel in 1975. He won the open pairs in 1962 and 1973, the men's pairs in 1975 and 1980, the individual in 1977 and the mixed pairs (with his wife Jean) and open teams in 1982 (when he was 70). As with the teams, he was usually in the places if not the winner. He was captain of the Western Australian open team at the ANC in 1958 and 1961-63 and a member of the team in 1964-66, 1969, 1973 and 1975-76. In all, he represented the state eleven times.
In international competition, Hans entered the record books, as, to this day, Australia's most successful non-playing captain. He was non-playing captain of the Women's teams that won the Far East championships three years in a row between 1973 and 1975 and won again in 1977. He was also non-playing captain of the women's team that came fourth in the Far East in 1972 and competed at the World Open Team Olympiad in 1976.
Hans also became the first Western Australian to captain an open team at the Far East Championships in 1982.
Performance at the table though was only one aspect of Hans' contribution to bridge. He was the first in Australia to have a regular bridge column (in the West Australian) from 1964 and published articles in Australian Bridge.
He was long prominent in administration while still playing. He was present at the first meeting to form an association in WA in 1939 but was not among the early office holders because of the war and his status as a German refugee would not have made participation easy. He was President of the old association in 1961, 1962 and 1964 and on the committee most other years. He was President of the restructured Bridge Association of Western Australia (BAWA) from 1975-78 and Secretary from 1978 until his death in 1983.
Hans is remembered appropriately in the Hans Rosendorff Memorial Women's Teams, a premier event that has traditionally attracted strong interstate competition to Perth (the first winners were the team of Norma Borin, Ailsa Tandy, Lidia Beech and Margaret Bourke); and the ABF's Committee of Honour. The ABF also donated funds to the James O'Sullivan Fund in his memory.