He returned to his country and became private secretary and interpreter to the Emperor Menelik II, who defeated the Italian colonial army in 1896 at the Battle of Adwa.
Becoming an important member of Menelik's entourage, Heywät served as a senior counsel and advised on and was a strong proponent of Ethiopia's modernisation.
Deeply concerned with the state of the Ethiopian economy, and understanding the economic importance of a productive middle class, Heywät pushed for structural social, political, and economic reform, which are partially reflected in efforts to remove unjust taxation and patrimonialism, while bureaucratic rationalism, the prohibition of slavery, and the elimination of noble privileges were promoted.
Following Menelik's death and the 1916 coup, he was first appointed controller of the (French built) railways and later collector of customs in Dérre Dawa, where he died.
[3][4] He published two majors works in Amharic, the Ethiopian national language: "Mengistna ye Hizb Astadadar", published in 1924 after his death and translated into English in 1995 as "State and Economy of Early 20th Century Ethiopia"; and in 1912, "Atse Menilik na Ethiopia", which was translated into French in 1993 as "L'Empereur Menelik et L'Ethiopie".