Cavit was born in Salonica, then in the Salonica Vilayet of the Ottoman Empire. His father was Naim, a merchant, and his mother was Pakize; they were cousins. He was of Dönmeh descent. Cavit was educated in economics in Constantinople. Following his graduation, he worked as a bank clerk and later as a teacher. Later he became an economist and newspaper editor. Having returned to Salonica, Cavit Bey joined the Committee of Union and Progress. After the proclamation of the Second Constitution in 1908, he was elected deputy of Salonica and Kale-i Sultaniye into the parliament in Constantinople. Following the 31 March Incident in 1909, Cavit Bey was appointed minister of finance in the cabinet of Grand VizierTevfik Pasha. Following the orchestrated Black Sea Raid on Russian ports in 1914, Cavit resigned. He remained an influential figure in the Empire's dealings with Germany until he returned to his post in February 1917. Up to the Armistice of Mudros in 1918 following the World War I, Cavit Bey played an important role in the CUP. Cavit Bey represented the Ottoman Empire in postwar financial negotiations in London and Berlin.
Republican period
In 1921, Mehmet Cavit Bey married Aliye Nazlı, the divorced wife of a prince. In 1924, their son Osman Şiar was born. After Cavit Bey's execution, his son was raised by his close friendHüseyin Cahit Yalçın. Following the enactment of the Surname Law in 1934, Osman Şiar adopted the surname Yalçın. In the early period of the Republican era, Mehmet Cavit Bey was charged with involvement in the assassination attempt in Izmir against Mustafa Kemal Pasha. After a widespread government investigation, Cavit Bey was convicted and later executed by hanging on August 26, 1926 in Ankara. Thirteen others, including other CUP members Ahmed Şükrü and Ismail Canbulat, were found guilty of treason and hanged. The letters which Cavit Bey wrote to his wife Aliye Nazlı during his imprisonment were given to her only after his execution. She had the letters published later as a book entitled, Zindandan Mektuplar. In 1950, Cavit Bey's remains were transferred and reinterred at the Cebeci Asri Cemetery in Ankara.