Born in the Gaza Strip in 1958, Shalah left to Egypt to pursue his study in the field of economics. (Read : Former head of Islamic Jihad dies at hospital)
During his study in Egypt, Shalah met with Palestinian activist Fathi Shqaqi with whom he co-founded the Islamic Jihad group.
Graduating from university in 1981, he returned to Gaza where he became a professor of economics at the Islamic University.
Shalah was known for his fiery sermons against the Israeli occupation, which prompted Israeli authorities to put him under house arrest and banned him from teaching.
In 1986, Shalah traveled to the UK to pursue his post-graduate studies in economics and obtained his PhD in economics in 1990.
In 1993, he left to the US where he worked as a teacher at the University of South Florida for two years before travelling to Syria in 1995 where he worked with Shaqaqi to found Islamic Jihad group.
Following the assassination of Shaqaqi in Malta in 1995 by Israeli agents, Shalah was elected the secretary-general of Islamic Jihad group. He remained in this post until 2018 when he suffered health problems.
Shalah was succeeded by Ziad al-Nakhalah as the new leader of Islamic Jihad.
US authorities added Shalah to a terrorist list in 2003, and the FBI added his name to its wanted list in 2017.
Shalah was a staunch advocate of the holy city of Jerusalem, which was occupied by Israel in 1967.
“Jerusalem is part of my religion,” he had said in an interview.
He had also championed several initiatives to heal the rift between rival groups Hamas and Fatah, but without success.