On Tuesday, airport police had already detained and deported American anti-war activist Medea Benjamin, also part of the delegation, who told AFP police broke her arm.
Maguire said she arrived at Cairo airport on Tuesday night with fellow activist Ann Patterson.
"We were taken to the detention centre and questioned and held for eight hours, and were told we would not be allowed entry into Cairo and would be put on a plane," she told AFP by telephone from Britain after her expulsion.
She said police were polite but gave no reason for barring her, while an airport official told AFP she had been blacklisted.
Maguire, born in 1944, won the 1976 Nobel Peace Prize with Betty Williams for founding a peace group to resolve the conflict in Northern Ireland.
She has become a vocal supporter of the Palestinians and was expelled from Israel in 2010, after trying to enter the blockaded Gaza Strip aboard a ship with other activists.
The delegation of activists that will try to enter Gaza through the Egyptian Rafah border crossing was meant to be led by Djamila Bouhired, an icon of the Algerian war of independence from France.
Bouhired had been expected to arrive at 1800 GMT on a flight from Paris, but did not do so.
Meanwhile, about 15 other activists were barred from leaving the airport, their comrades said, and it was not immediately clear if they too would be deported.
Egypt controls the only border crossing with Gaza that bypasses Israel, and is accused of colluding with the Jewish state to blockade the territory ruled by the militant Islamist group Hamas.
-Complying 'with blockade'-
The border crossing is opened irregularly.
"I think it's sad, what they've done," Maguire said of the reception she and the other activists received in Egypt.
"It is an example and confirmation of the Egyptian government's compliance with the blockade of Gaza."
In 2006, a year after Israel withdrew its soldiers and settlers from Gaza, militants abducted soldier Gilad Shalit, and the Jewish state slapped a blockade on the enclave.
It tightened the blockade in 2007 when Hamas, which says it seeks the destruction of Israel, seized control of Gaza after routing forces loyal to Palestinian president Mahmud Abbas.
Egypt refuses to recognise Hamas's authority in Gaza and only infrequently allows some aid through the Rafah crossing.
Cairo says the crossing is meant for people, not goods, and a 2005 agreement between Israel and the Palestinians stipulates that Abbas's forces should be present at the passage.
Pro-Palestinian activists from abroad protested in Cairo in 2010 when they were prevented from entering Gaza.
The government of then president Hosni Mubarak eventually allowed some of the activists to cross.