It is widely believed that Haniya was chosen for the prime ministerial position because he is regarded as a good communicator and is based in Gaza, which is not directly controlled by the Israeli army, giving him freedom of movement, including the ability to travel abroad.
Palestinians in the West Bank have limited freedom of movement, the area continuing to be tightly controlled by the Israeli occupation army.
Haniya was born in 1962 to a poor refugee family at the Shati refugee camp, just outside Gaza City, where his family - like almost 70% of Gazans - lived on monthly stipends provided by the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA).
In 1983 he joined the Islamic University of Gaza, where he soon joined the Islamic Student Bloc, a precursor to Hamas.
In 1987 he graduated with a BA in Arabic literature. In December that year he joined the intifada (uprising), which began when an Israeli truck ran over six Gaza labourers.
It was at this time that Hamas, an acronym for Harakatu al-Muqawama al-Islamiya (Islamic Resistance Movement), was founded by a group of Muslim Palestinian intellectuals and activists affiliated to the Muslim Brotherhood and led by Shaikh Ahmad Yasin.
Haniya was arrested for a short time in 1987, and again in 1988, on charges of involvement in the uprising and resisting the Israeli occupation.
In 1989, Haniya was re-arrested and sentenced to three years in jail in connection with his role in the resistance.
On his release in 1992, Haniya was deported to Marj al-Zuhur in southern Lebanon along with more than 400 Muslim activists from the West Bank and the Gaza Strip.
After the creation of the PA, Haniya and other Hamas leaders were arrested by PA security agencies.
In 1997, Haniya became a close
aide to Shaikh Yasin (above)
The PA saw Hamas' often violent opposition to the Oslo Accords as a direct threat to a "national scheme".
In 1997, following the release of Yasin from an Israeli jail, and the failed Mossad assassination attempt in Amman on Khalid Meshaal, a Hamas leader, Haniya became a close aide and confidante of Yasin.
In 2001, a few months into al-Aqsa Intifada, Haniya consolidated his position and became one of Hamas' political leaders, probably occupying the third place after Yasin and Abd al-Aziz al-Rantisi. Al-Rantisi was assassinated by Israel in March 2003.
In September 2003, Haniya and Yasin were slightly wounded when an Israeli warplane bombed a house where the two had been dining in downtown Gaza.
Yasin was assassinated by Israel in a missile attack in April 2004.
Calm and soft-spoken, Haniya is considered among the more pragmatic figures in Hamas. According to Atif Udwan, professor of political science at the Islamic University in Gaza, Haniya is a good listener.
"He respects his interlocutors and doesn't like static attitudes. He is a very approachable person."
The fact that Hamas has chosen him as the next Palestinian prime minister may suggest that the movement is edging towards moderation.
Haniya is a strong proponent of Palestinian national unity. He reportedly played a main role in preventing a brief showdown between Fatah and Hamas in 2005 from getting out of control.
Haniya, unlike some other Hamas leaders, has avoided suggesting "the destruction of Israel".
"What we've got instead are more settlements, more occupation, more roadblocks, more poverty and more repression"
Speaking on the Oslo Accords
He said in Gaza a few days after Hamas' electoral victory that Hamas would seek a modus vivendi with Israel if it recognised a Palestinian state within the 1967 borders.
Haniya has also voiced a willingness to abandon violent resistance if Israel reciprocated by stopping violence and repression against Palestinians.
One of Haniya's main objections to the Oslo accords, reached by Israel and the PLO in 1993, is that the PLO granted Israel a "free" recognition without a reciprocal Israeli recognition of a Palestinian state.
In an interview last year, he said the US and the international community duped the Palestinians by telling them that the Oslo Accords would end the Israeli occupation and give them an independent state.
"What we've got instead are more settlements, more occupation, more roadblocks, more poverty and more repression," he said.