Fayyad was never elected to his post and he is not a member of either Hamas or Fatah. However, it is because of Fayyad that West has been enamored with the idea that Palestinian Arab statehood is possible over the past couple of years.
Fayyad has no terrorist history. He has a Western education and outlook. He has largely corrected the more egregious abuses and corruption that was endemic under Arafat.
And (for those very reasons!) he is hugely unpopular in both Hamas and Fatah circles.
The remarkably small and vague agreement signed by Hamas and Fatah includes this section:
Fatah and Hamas Agree to form a Palestinian government and appoint a [caretaker] prime minister and [government] ministers before the elections.
Which means that Hamas has veto power over Fayyad.
And Hamas is insisting that they do not want him as PM:
Hamas has insisted on the departure of Salam Fayyad, the Palestinian prime minister favoured by Israel and the west, under a deal agreed with its rival faction Fatah for a unity government, according to sources in Gaza.
The existing Fatah dominated PA is trying to deny the story, but since the two groups have not yet started to negotiate anything concrete it is pretty clear that absent huge external pressure, Fayyad will be gone. (And if they keep him it would only be until the minute they don't need him anymore, likely in September.)
Western nations that have been encouraged by Fayyad's actions need to understand that he will not be part of any "Palestine" and that the theoretical state would be dominated by corruption and terror.
Would the World Bank have written their fawning report on Palestinian Arab statehood had Fayyad not been running the PA's internal affairs?