Abbas had demanded a complete halt to Israeli settlement building as a condition for resuming talks suspended in December 2008. The Arab League and PLO decisions gave him political backing for indirect negotiations without a freeze.
Yasser Abed Rabbo, a senior PLO official announced the Palestinians would embark on US-mediated talks but expressed deep scepticism over the prospects of success.
He told reporters: "The Palestinian leadership has decided to give an opportunity for the American suggestion to hold indirect talks between the Israeli and Palestinian sides."
He said the indirect talks would be limited to four months as proposed by the Arab ministers and should focus first on final borders.
He said: "The Arab position was clear. If there is no real progress within four months, there are different options, including going directly to the UN Security Council."
Mitchell, who has been trying to broker a resumption of peace talks for a year, met Binyamin Netanyahu, the Israeli prime minister, in Jerusalem for more than two hours on Sunday.
Netanyahu told reporters before his meeting with Mitchell: "If there is a desire to get to direct talks through a corridor then I think the sooner the better."
Mitchell said he hoped for a "credible, serious, constructive process" leading to comprehensive peace in the Middle East.
A brief statement issued by Netanyahu's spokesman after the session said the Israeli leader and Mitchell "had a good conversation ... on moving the diplomatic process forward".
The statement said Netanyahu and Mitchell would meet again on Monday before the envoy sees Abbas.
Many observers and politicians doubt that the indirect talks can succeed where years of negotiations have failed.