Johannis III (or Yohannes III) was the last of the elder "Gondar" line of the Solomonid Dynasty to reign over Ethiopia. He was largely a figurehead, with real power in the hands of the "Enderase" or Regent, Ras Ali II a princeling of the Oromo ruling family of the district of Yejju . Ras Ali had compelled Emperor Yohannis to marry Ras Ali's mother, the formidable Empress Mennen Liben Amede who dominated both her husband and her son.

During the various wars between Ras Ali and his leading rival for power, Dejazmatch Wube of Simien , Emperor Yohannes was deposed and restored several times between 1840 and 1851, often being replaced by his cousin Sahle Dengel as Emperor. Finally, the son-in-law of Ras Ali, Kassa of Kwara, defeated both Ras Ali and Dejazmatch Wube, and usurped the Imperial throne as Tewodros II, Emperor of Ethiopia. Yohannes III agreed to step down from the throne on the condition that the new Emperor guarantee that he would not ever be made to reunite with his much hated wife, Empress Mennen.

Ex-Emperor Johannes III then faded into obscurity, dying a very impoverished man sometime in the early 1870s. It is often said that he converted to Roman Catholicism at the end of his life, and wrote a letter to Napoleon III asking for financial relief.