Under the declaration's provisions, the 183 countries who attended the summit have agreed to strengthen humanitarian interventions, hold further trade talks and increase agricultural investment.
Henri Djombo, Congo's forestry and environment minister and chairman of the summit committee that agreed the declaration's final wording, said: "We have adopted the text."
The summit's plenary session must now also adopt the declaration, something UN officials said was a formality.
However, Argentina said that it could not accept the text and suggested its objections be put in an annex.
Mark Seddon, Al Jazeera's correspondent in Rome, said the delegates had been struggling to agree the final declaration.
"This has taken a lot longer than anyone expected. There's a consensus that this was a good event to have in that it has concentrated the eyes of the world on the problem," he said.
"However, in terms of concrete deals, it has not been a great success."
Earlier on Thursday, small farmers' groups said they had reacted with "disgust" to the conclusions of the summit.
"We are dismayed and disgusted to see the food crisis used to further the policies that have led us to the food crisis in the first place," Maryam Rahmanian from Iran's centre for sustainable development said.
Dozens of non-governmental organisations and small farmers' groups held a forum in Rome this week to coincide with FAO summit.
Having seen a draft text of the FAO declaration on Wednesday, Rahmanian said that "will not fill any plate".
"The recommendations for more liberalisation would lead to more violations of the right to food," she said in a statement.
Since the 1996 world food summit, "we have warned continually that the current model would lead to a food crisis, and it has."
The farmers' groups criticised multi-national food corporations whose profits have shot up through the crisis.
Flavio Valente, a Brazilian activist, said it was "about time we treated this as a crime against humanity".
However, the UN and some food agencies have hailed the summit a success.
"The most important thing about the summit is that it has focused attention on the world leaders and on something that has been ignored for too long," Matthew Wyatt, from the International funds for agricultural development, said.
"We've let investment in agriculture drift terribly. In 1979 it was 18 per cent of all aid. Now it's less than three per cent, that's absolutely ridiculous... We have to reverse that."
Ban Ki-Moon, the UN secretary-general, said: "I think these kinds of conferences are important to put together people discussing. I think it's more important outside the big room and the official speeches.
"It's important to know each other because many times we meet in the operation and if we know each other we can work better together," Massimo Barra, a Red Cross representative, said.