Saudi Arabia, Bahrain and the UAE have agreed to return their respective ambassadors to Qatar.
In an unprecedented public move, the three Gulf states had recalled their ambassadors in March, accusing Doha of failing to abide by an agreement not to interfere in one another's internal affairs.
The announcement to return the envoys followed a surprise meeting between representatives of the states in Saudi Arabia late on Sunday.
A statement posted on the Gulf Co-operation Council's official websitesaid that the agreement aimed to "solidify the unity of the GCC".
A GCC statement on Sunday said the agreement for the ambassadors to return to Doha "promises the opening of a new page that will present a strong base, especially in light of the sensitive circumstances the region is undergoing".
It said these circumstances "require extra effort" to safeguard the Gulf's security.
"Based on this, Saudi Arabia, the UAE and Bahrain have decided to return their ambassadors to Doha," it said.
The three states fell out with Qatar in part over Doha's alleged support of the Muslim Brotherhood. Qatar said it backs all Arabs, not just Brotherhood members.
Saudi Arabia has banned the Brotherhood, accusing it of seeking to overthrow the Gulf monarchies.
On Sunday, the UAE designated the Brotherhood and about 80 other groups as "terror organisations".
Speaking to Al Jazeera from Beirut, Joseph Kechichian, a senior writer at Gulf News, said the Muslim Brotherhood was not the only point of disagreement between the GCC countries.
"There are other issues at stake here. A major dispute between the members of the GCC has been what to do with the rising [number] of extremists whether it is in Yemen, whether it is Syria, whether it is in Egypt. There was a great deal of disagreement among all the member states. Somehow a decision has been made to make compromises. "
Source: Al Jazeera and agencies