The rare visit came just days ahead of a key summit between the rival Palestinian movements Fatah and Hamas, which are looking to cement a stalled unity deal that has drawn fierce opposition from Israel and Washington.
It was the first time the monarch visited the West Bank's political capital since August 2000, and came just days before the Palestinian leader was due in Cairo to meet exiled Hamas chief Khaled Meshaal.
But officials said little about the reasons behind the high-level visit, which saw the Jordanian monarch flying in by helicopter for a brief stay of little more than two hours.
"This was an important and historic visit with a message of support," Abbas told reporters after the king's departure, without revealing what was discussed.
"We thank the king for his strong support for the Palestinian Authority and the Palestinian cause particularly at this time."
Speaking to reporters as the two leaders held closed-door talks, Nasser Judeh, the Jordanian foreign minister, expressed support for both the Palestinians' UN membership bid and for moves to cement a unity deal between Hamas and Fatah.
"The king has always said that strength comes from unity of the Palestinian front," he said.
"Jordan's goal is to support the Palestinian Authority and the Palestinian cause and we will make every effort for the Palestinian cause and the unity of the Palestinian front."
Standing beside him, Palestinian foreign minister Riyad al-Malki said reconciliation was of the greatest importance.
"For us there is no greater interest than the reconciliation and the end of the division," he said.
Earlier an Abbas adviser Nimr Hammad described the timing of the visit as "very important" and said they would discuss "all the political developments between us and the international community in order reach a common Palestinian-Jordanian understanding on the issues."
Talks had been expected to touch on the Palestinian bid to secure full state membership at the United Nations, and on the forthcoming Hamas-Fatah meeting in Cairo – both of which have met with strong US and Israeli opposition.
Under terms of their unity deal, Fatah and Hamas were to piece together an interim government of politically unaffiliated technocrats who would prepare for presidential and legislative elections within a year.
But the caretaker government was never formed, with the two sides bickering over its composition and over who would take up the role of premier.
However, the two sides appear to have reached some form of agreement which is likely to be made public after they meet in the Egyptian capital later this week, officials say.
King Abdullah paid his first visit to the Palestinian territories in May 1999 just months after being crowned king, meeting the late leader Yasser Arafat in Gaza.
In April 2000, he made his first visit to Ramallah and returned four months later, which was the last time he visited the city.
A senior Israeli official, who said they were not informed of Abdullah's plans, welcomed the West Bank visit.
"We have repeatedly called in the past for Arab leaders to travel to Ramallah in order to strengthen the peace process. Unfortunately, almost none of them have come," he said.