Grunis (born 1945) was born in pre-state Israel. In 1962, he was drafted into the Israel Defense Forces where he served for four years.
In 1969, Grunis graduated from the Hebrew University of Jerusalem's School of Law and he would later go on to receive his Master of Law degree from the University of Virginia in the United States and his Ph.D. from York University in Toronto, Canada.
In 2003, Grunis was appointed as a justice on the Israeli Supreme Court.
On February 28, 2012, upon the retirement of Supreme Court President Dorit Beinisch, Grunis was officially appointed as President of the Supreme Court. His appointment was made possible after the Knesset passed the so-called "Grunis Law" which enables the selection committee to designate a new judge for President who is within three years of the mandatory retirement age of 70.
In a speech to mark the occassion, Grunis said:
"The State of Israel is a Jewish and democratic state, and it must preserve the Jewish values and protect the ways of democracy ... The judges are performing a divine service, they act out of a sense of great responsibility. We all deal with providing a special service, led by a sense of vocation."