His father Yehoshua Yellin was one of the founders of the Nahalat Shiv'a neighborhood in Jerusalem and his mother Serah was the daughter of Shlomo Yehezkel Yehuda, the son of Ezekiel Judah, a Rabbi and educator from Iraq.

At the age of 14, Yellin started writing a newspaper, Har Tziyon ("Mount Zion"), which was published in one copy twice a month; he sustained it for 43 issues.

The committee disbanded after one year, but was reestablished in 1904 when school teachers complained about the lack of Hebrew terminology.

In 1903 he participated with Menachem Ussishkin in the founding of the Assembly of the Land of Israel (הכנסייה הארצישראלית)—an attempt to create a representative body of the Jews in the Yishuv.

Like his younger brother Shlomo Yellin, David was a staunch supporter of the Ottoman Empire in the years after the Young Turk Revolution.

[1] In 1913, at the time of the War of the Languages in the Yishuv, Yellin resigned from the teachers college that was sustained by the Hilfsverein der deutschen Juden (Aid Society of German Jews), which supported German-language professional education in the Technion, and founded the Hebrew school for teachers.

As a consequence of these events and the Mandatory Palestine administration's handling of Jews, Yellin and his wife wrote in 1939 a letter to the High Commissioners for Palestine and Transjordan in which they explained why they are returning the awards that they received from the British government: The award of honor was given to me by this government, for which political considerations are more important than any feeling of morality, and which cause it to assist those who killed and mauled not only my people (among them my innocent son!)

[2][3] Yellin was one of the central people in the process of the revival of the Hebrew language, and particularly active in coining neologisms.