Jamie McGoldrick, who is also the UN's humanitarian coordinator in the occupied Palestinian territories, will travel to Bahrain for the June 25-26 conference, said UN spokesman Farhan Haq.
President Donald Trump's son-in-law Jared Kushner has been drafting the long-awaited peace plan that has already been rejected by the Palestinians, who expect the proposals to heavily favor Israel.
The plan is aimed at providing economic opportunities for the Palestinians, but Kushner has hinted that it will not endorse international calls for the creation of a Palestinian state.
Several UN resolutions have enshrined the two-state solution to the Israeli-Palestinian conflict as the path to a peace settlement.
The Palestinian Authority has already said it will boycott the Bahrain conference after it cut ties with the US administration over Trump's recognition of Jerusalem as Israel's capital.
The United Nations said in late May that it was not planning to send a representative to the Bahrain conference.