Leopold Gratz (November 4, 1929, Vienna – March 2, 2006, Vienna) was an Austrian politician.
Born in Vienna, Gratz was a law graduate and a member of the Austrian Social Democratic Party (SPÖ). From 1963 to 1966 he was a member of the Bundesrat, from 1970 to 1971 Federal Minister of Education and the Arts. From 1966 to 1973 he served as a member of The National Council of Austria and from 1986 to 1989 also as the First President of The National Council of Austria, from 1971 to 1973 as the leader of the Socialist group in the Parliament of Austria.
From 1973 to 1984 he was Mayor of Vienna and head of Vienna's municipal government. In 1976, he became chairman of the Vienna chapter of the Austrian Social Democratic Party. From 1984 to 1986 he was the Minister of Foreign Affairs, and from 1986 to 1989 he was the First President of the Nationalrat. His term of office as Mayor of Vienna was overshadowed by the "Bauring" affair and the scandal around the construction of the Vienna General Hospital. He decided to resign from the government in 1989 following another scandal, the Udo Proksch affair. Burdening his authority as the second highest politician of the Republic of Austria, Gratz well-meaningly had tried to protect his close friend Udo Proksch, who later was convicted of the murder of six seamen and received a life sentence, from criminal prosecution. After Gratz has decided to abandon politics, he remained a member of the party executive committee of the SPÖ Vienna as well as president of the International Conference on Kampuchea (ICK) by request of the United Nations Organization (UNO).