The beginning of his reign marked the transition of Montenegro from a traditional theocratic form of government (Prince-Bishopric) into a secular Principality.

His charismatic elder brother, Grand Voivode Mirko Petrović-Njegoš led a 7,500 strong army and won the crucial Battle of Grahovac against the Turks (between 7,000 and 13,000) on 1 May 1858.

The glory of Montenegrin weapons was soon immortalized in the songs and literature of all the South Slavs, in particular the Serbs in Vojvodina, then part of Austria-Hungary.

Montenegro gained Grahovo, Rudine, Nikšić's Župa, more than a half of Drobnjaci, Tušina, Uskoci, Lipovo, Upper Vasojevići, and the part of Kuči and Dodoši.

His educated and wealthy wife together with Russia's failure to live up to promise for Montenegro's international recognition of full sovereignty, heavily influenced his Francophile attitude.

At the same time, all major European powers worked to undermine Russian influence in Southeastern Europe, which was the strongest in Montenegro.

Knowing the mood of his people, Danilo refused to compromise on the sovereignty of Montenegro averting to the extent the pressure from Europeans.

In the subsequent Congress of Paris in 1856, Russian government representatives did not have enough strength to support Montenegrin demands for independence and territorial enlargement.

By the same token, Napoleon III hoped that this would bring Montenegro closer to French influence to the expense of Russia.

The plans to organize the elimination of the Prince were coined by the Montenegrin emigration led by Stevan Perović Cuca and assisted by foreign powers.