Officials say the majority of the group’s Shura council members voted for him.
Mashaal had previously indicated he would not seek another term, but officials told Maan news agency that Arab and Palestinian figures asked him to seek the top spot once again.
The 56-year-old has headed the political bureau of Hamas since 1996.
His re-election could revive stalled reconciliation efforts between Hamas and political rival Mahmoud Abbas, AP says.
Hamas seized the Gaza Strip in 2007, leaving Abbas with a self-rule government, the Palestinian Authority, in parts of the West Bank. Both sides have become entrenched in their territories, hampering reconciliation.
Meshaal, set foot in Gaza for the first time in December since leaving the West Bank in 1967.
Meshaal ran the group from exile in Damascus from 2004 a few months before he left the Syrian capital because of unrest in Syria and to avoid pressure from Syrian authorities to side himself with President bashar al-Assad, according to sources. He now divides his time between Qatar and Cairo.
Hamas continues with its view that it will not recognize the Jewish state officially, and it is viewed as a terrorist group by Israel, the United States and most Western governments.