In 1858 he was sent to Saint Petersburg on a special mission to seek the support of Russia in the threatening Franco-Austrian War against Napoleon III.

[3] Károlyi was appointed Envoy Extraordinary at Berlin in 1866 at the time of the rupture between Prussia and Austria, and after the Seven Weeks War was responsible for the negotiation of the preliminaries of peace at Nikolsburg.

[6] In January 1864, he wrote to the Austrian Foreign Minister, Count Johann Bernhard von Rechberg und Rothenlöwen: "the surest sign not only of the political but of the social divisiveness which is inherent in the internal life of the Prussian state, to wit, the passionate hatred of different estates and classes for each other.

This antagonism... which places in sharp opposition the army and the nobility on one hand and all the other industrious citizens on the other is one of the most significant and darkest characteristics of the Prussian Monarchy.

Upon his death, his insignia of the Order was returned to the Emperor, before it was awarded to his kinsman Sándor Károlyi by Franz Joseph I, as it could only be held by one member of a family at the same time.