Ibrahim Munir, the leader of the outlawed Muslim Brotherhood, died on Friday, two years after taking the role.
The organisation said in a statement that Munir had lived in London for decades and was 85 years old.
He had lived in exile for most of the last 40 years.
The Islamist movement was founded in Egypt and took power in a presidential election in 2012. A year later that presidency was brought down by mass protests against the organisation's rule.
The Muslim Brotherhood high command has since used its position overseas to try to consolidate after the loss of power and Munir was central to those efforts.
The group's spiritual leader Yusuf Al Qaradawi died in September. He was sentenced to death by an Egyptian court in absentia in 2015 along with other Egyptians affiliated with the Muslim Brotherhood in a case relating to a 2011 mass jail break.
He was also banned in several countries, including France and the UK since 2012 after advocating for suicide bomb attacks against Israelis. Saudi Arabia, the UAE, Bahrain, and Egypt labelled him as a terrorist.