Al-Messiri, who earned his master's and doctorate degrees in the US, was considered one of the Arab world's leading experts on Jewish and Israeli affairs, compiling an eight-volume encyclopedia on Jews, Judaism and Zionism.
"Dr. Messiri was a giant intellectual pillar of Arab culture," Amin Eskander, a Kefaya leader, told Al Jazeera.
He has also published works about philosophy, secularism and modernism.
As leader of the Kefaya movement, Al-Messiri also spent a lot of time on the streets, protesting Egyptian policies.
Fighting against policy
|Al-Messiri is most famous for an encyclopedia on Judaism and Zionism
"He was always there in the middle of demonstrations, undeterred by repression and threats," Eskander said. "He will always be present through his work and legacy among Arab intellectuals and in the hearts of the Egyptian people."
In January, Al-Messiri, his wife and other members of the Kefaya movement were abducted before a demonstration in an Egyptian town square against rising prices and the government's plan to cut subsidies on basic commodities.
"They drove for almost two hours then dropped us in a totally deserted place and left," Al-Messiri told Egyptian press. The group eventually flagged down a bus and returned to town, but security forces had already dispersed the crowd, he added.
The professor, a former communist and member of the Muslim Brotherhood, was also briefly detained in April.
Who will replace Al-Messiri as general coordinator of Kefaya is not immediately known.