He attended elementary and secondary school in the city and then at the Marjan Preparatory School in Istanbul, Turkey.
He was appointed to the Arab Higher Committee in 1945 and was the chairman of the Palestinian Arab paramilitary scout movement, al-Najjada (1945–47). He enrolled at the Mulkiyya College in Istanbul as a result. He was consequently recognized by the Ottoman Education Ministry and given a grant to learn at the Sorbonne in Paris.
There he received a degree in literature and education. Al-Tamimi served in the local administration of the Ottoman Empire as a principal of a government-run school in Beirut. In 1916, during World War I, Ottoman officials ordered al-Tamimi to gather information for a general "guide book" on the southern half of the Beirut Province, namely Jabal Nablus.
He was elected to the central committee of al-Fatat in December 1918. He also became chairman of the Jaffa branch of the National Committee. He led efforts to merge the al-Najjada and al-Futuwa youth movements in Palestine in 1946.
In May 1946, the Arab League dissolved the AHC and al-Tamimi was not part of the replacement Arab Higher Executive, under Amin al-Husayni's chairmanship, which was based in Cairo. After the Bloudan Conference of 1947, he was reappointed to the reformed AHC by Jamal al-Husayni on January 5, 1947. He was part of the Palestinian delegation to the Arab League in February 1948 aimed at obtaining military, political, and moral support for the Palestinian cause from the Arab states.
In the early 1940s, he joined the Palestine Arab Party and represented the party on the Arab Higher Committee in 1945.
In July 1919, following the Arab Revolt (1916–18) which succeeded in gaining Arab independence, al-Tamimi along with Izzat Darwaza, Sa'id Haydar and other members of al-Fatat's inner circle formed a group in the Syrian National Congress that rejected the establishment of any foreign mandate (British or French) in Greater Syria, claiming it would only be a "disguised form of imperialist penetration.".