Yiannis Grivas (also spelled Ioannis Grivas) (born 1923), Greek judge, was a non-party interim Prime Minister of Greece.

Grivas was born in Kato Tithorea in the region of Lokris. He studied law at the University of Athens and in 1954 he became a judge. In 1979 he was appointed to the "Areios Pagos"(Supreme Court of Greece for Civil and Criminal Cases). He became vice-president of the court in 1986 and president in 1989. He was a member of the court that tried the leaders of the 1967 military regime after its fall in 1974.

In 1987 Grivas was the president of the special court that tried a vice-minister of the government of Andreas Papandreou on corruption charges.

In 1989, when the Greek Parliament was deadlocked between the PASOK and New Democracy parties, the Constitution requiring that the President of one of Greece's Supreme Courts be appointed interim Prime Minister, Grivas agreed to head a caretaker government to preside over fresh elections. He took office on October 11, 1989. After the elections produced another deadlocked Parliament, he resigned on November 23, 1989, in favour of Xenophon Zolotas, who formed a non-party government. Grivas retired in 1990.