Hisashi Owada, Crown Princess Masako's father and a former administrative vice minister for foreign affairs, was appointed president of the International Court of Justice in the Hague on Friday.
It is the first time the ICJ, an organ of the U.N., has had a Japanese chief, the Foreign Ministry said.
Owada, 76, has served as one of the 15 judges of the ICJ since February 2003. His term as head of the international court will last three years.
The ICJ's role is to settle, in accordance with international law, legal disputes brought to the court by nations.