Nabil Abu Rudeineh will serve as deputy prime minister and information minister, the government said.
The move comes amid talk of fresh attempts at reconciliation between Abbas's Fatah and Hamas, which runs the Gaza Strip.
Hamas said it ran contrary to those efforts, which have repeatedly failed in the past.
"Any reconciliation agreement must be submitted to a unity government and not to a Fatah government," said Hamas spokesman Sami Abu Zuhri.
Prime Minister Rami Hamdallah told journalists the appointment was part of the Palestinian Authority's efforts to develop the information sector.
Abu Rudeineh will retain his position as spokesman for the Palestinian presidency.