His mother, Saada Gillon (née Frumkin), was born in Ottoman Judea to which her ancestors immigrated from the Russian Empire in the 19th century, likewise Gillon's maternal great grandfather was Israel Dov Frumkin, a pioneer of Hebrew journalism who arrived 1859 (When Judea was part of Ottoman Syria).

His maternal grandfather, Gad Frumkin, was one of the first trained attorneys in British-Palestine (a novel parcellation after WW1), who was the only Jewish judge on the Supreme Court of Palestine during the British Mandate era and was also a member of the Hebrew University of Jerusalem's Board of Governors from the 1930s until his death.

His maternal grandmother, Chana Frumkin, was the daughter of Aharon Eisenberg, a pioneer of the First Aliyah who was one of the founders of Rehovot, and was the President of B'nai B'rith in Jerusalem.

Colin served as State Attorney, and Hebraized his name from Gluckman to Gillon at Prime Minister David Ben-Gurion's insistence.

From 1987 to 1989, he attended the National Security College, serving in a number of senior positions during his studies for an MA in political science and public administration.

"During his tenure, and until the Israel High Court of Justice ruled against such methods in 1999, GSS interrogators were officially sanctioned to use 'moderate physical pressure' on detainees (the vast majority of them Palestinians)," according to Amnesty International.

Secret government guidelines set down what "moderate physical pressure" and "increased physical pressure" allowed; according to court testimonies of GSS members themselves, this included subjecting detainees to sleep deprivation, prolonged shackling in painful positions, hooding with filthy sacks, being forced to squat like a frog (gambaz[what language is this?])

During Carmi Gillon's period of service with the GSS such methods of interrogation were used against several hundred Palestinian detainees every year, many of whom were later released without charge.

Gillon had been in Paris at the time of the assassination, and upon returning to Israel, immediately submitted his resignation to Acting Prime Minister Shimon Peres, who rejected it.

He told Danish media that Israel might have to re-introduce "moderate physical pressure" when interrogating suspected Palestinian terrorists.

One member of parliament, Centre Democrat leader Peter Duetoft, called opposition to Gillon's appointment "hypocritical" because Yasser Arafat, "the biggest terrorist", had recently visited Denmark without there having been similar objections.

Gillon has been a member of a number of boards of directors, including the Tahal Group, Danker Investment, and the Arab Israel Bank.