Samir Murqus, a liberal Coptic writer, was named assistant for democratic transition, officials announced.
Pakinam al-Sharkawi, who teaches political sciences at Cairo University, will be in charge of political affairs.
During his election campaign Mr Mursi said he would appoint Copts among his advisers, possibly as vice-president.
However, he named Mahmoud Mekki, a veteran judge who campaigned for judicial independence under Hosni Mubarak, as his deputy.
Copts, who make up about 10% of Egypt's 82 million people, were also disappointed that the new cabinet includes only one Christian.
The two other assistants appointed on Monday are members of the two Islamist parties which dominated parliament before it was dissolved in June after a court found the election law had been unconstitutional.
Imad Abdul Ghafour, the head of the ultraconservative Salafist Nour party, is in charge of relations with civil society, while Issam al-Haddad of the Muslim Brotherhood's Freedom and Justice Party, will look after external relations and international co-operation.
Mr Mursi also named on Monday the first 17 members of his "presidential advisory team", with whom he will hold regular meetings.
They include former presidential candidate Mohammed Salim al-Awwa, Muslim Brotherhood leader Essam al-Aryan, political expert Seif al-Din Abdul Fattah and writer Sekina Fouad.
Pakinam al-Sharkawi, who teaches political sciences at Cairo University, will be in charge of political affairs.
During his election campaign Mr Mursi said he would appoint Copts among his advisers, possibly as vice-president.
However, he named Mahmoud Mekki, a veteran judge who campaigned for judicial independence under Hosni Mubarak, as his deputy.
Copts, who make up about 10% of Egypt's 82 million people, were also disappointed that the new cabinet includes only one Christian.
The two other assistants appointed on Monday are members of the two Islamist parties which dominated parliament before it was dissolved in June after a court found the election law had been unconstitutional.
Imad Abdul Ghafour, the head of the ultraconservative Salafist Nour party, is in charge of relations with civil society, while Issam al-Haddad of the Muslim Brotherhood's Freedom and Justice Party, will look after external relations and international co-operation.
Mr Mursi also named on Monday the first 17 members of his "presidential advisory team", with whom he will hold regular meetings.
They include former presidential candidate Mohammed Salim al-Awwa, Muslim Brotherhood leader Essam al-Aryan, political expert Seif al-Din Abdul Fattah and writer Sekina Fouad.
