He joined the Colonial Department of the Foreign Office (Kolonialabteilung des Auswärtigen Amtes) and in 1898 was assigned as district judge in Dar es Salaam in German East Africa for a short period.

[5] In turn, tax revenues were enhanced, making the establishment of a public school system, the construction and the staffing of a hospital major successes.

The Samoan colony was on its way to self-sufficiency and had reached that achievement just before Solf was called to Berlin and was succeeded by Erich Schultz as Governor of German Samoa.

[6] The outbreak of World War I caused Germany's colonial possessions to be invaded by the United Kingdom (including the dominions), Belgium, France and Japan.

He resigned his post as Foreign Minister on 13 December 1918 with the onset of the German Revolution after news about the payment of about 1-million Mark and a 10.5-million Russian ruble mandate for a bank account at Mendelssohn & Co by the Russian ambassador to Germany, Adolph Joffe, to the Independent Social Democratic Party of Germany politician Oskar Cohn had become public.

From 1920 to 1928, he served as the German chargé d'affaires[10] and then ambassador to Japan; his tenure proved to be fruitful, as he was instrumental in restoring good relations between the two World War I enemies, which culminated in the signing of the German-Japanese Treaty of 1927.

On Solf's return to Germany and his retirement from government service, he became the Chairman of the Board of the Deutsches Ausland-Institut [de] based in Stuttgart.

Solf held centrist political views and joined the German Democratic Party (Deutsche Demokratische Partei).