"In these days it delights us as Palestinians to see the Palestinian flag flying in the heart of Lebanon, in the heart of the Lebanese people, and in the heart of every Lebanese who loves Palestine," the Lebanese Web site Naharnet.com quoted Abbas saying at Wednesday's ceremony.
The inauguration of the embassy came after the Lebanese cabinet officially recognized the state of Palestine and raised the level of diplomatic ties, the Web site said.
Abbas, accompanied by Lebanese Prime Minister Najib Miqati unveiled a plaque at the entrance to the building.
"We will go with Lebanon to the United Nations to seek a full membership for the state of Palestine at this international forum," Abbas said adding he hoped "to see the day when the Lebanese flag will be hoisted in Jerusalem."
"The Lebanese government will exert utmost efforts within its available resources to improve the living conditions of our Palestinian brothers residing in Lebanon," Miqati said.
Abbas, on a two-day visit to Beirut to garner Lebanon's support ahead of the Palestinian statehood bid at the United Nations in September, said so far, 122 of the 193 member countries support the Palestinians.
Lebanon takes over temporary presidency of the U.N. Security Council in September.