The negotiation among the Balkan states' governments started in the latter part of 1911 and was all conducted in secret. The treaties and military conventions were published in French translations after the Balkan Wars on 24–26 of November in Le Matin, Paris, France ^[7] In April 1911, Greek PM Eleutherios Venizelos’ attempt to reach an agreement with the Bulgarian PM and form a defensive alliance against the Ottoman Empire was fruitless, because of the doubts the Bulgarians held on the strength of the Greek Army.^[7] Later that year, in December 1911, Bulgaria and Serbia agreed to start negotiations in forming an alliance under the tight inspection of Russia. The treaty between Serbia and Bulgaria was signed on 29 of February/13 of March 1912. Serbia sought expansion to "Old Serbia" and as Milan Milovanovich noted in 1909 to the Bulgarian counterpart, "As long as we are not allied with you, our influence over the Croats and Slovens will be insignificant". On the other side, Bulgaria wanted the autonomy of Macedonia region under the influence of the two countries. The then Bulgarian Minister of Foreign Affairs General Stefan Paprikov stated in 1909 that, "It will be clear that if not today then tomorrow, the most important issue will again be the Macedonian Question. And this question, whatever happens, cannot be decided without more or less direct participation of the Balkan States". Last but not least, they noted down the divisions that should be made of the Ottoman territories after a victorious outcome of the war. Bulgaria would gain all the territories eastern of Rodopi Mountains and River Strimona, while Serbia would annex the territories northern and western of Mount Skardu.

The alliance pact between Greece and Bulgaria was finally signed on 16/29 of May 1912, without stipulating any specific division of Ottoman territories.^[7] In summer 1912, Greece proceeded on making "gentlemen's agreements" with Serbia and Montenegro. Despite the fact that a draft of the alliance pact with Serbia was submitted on 22 of October, a formal pact was never signed due to the outbreak of the war. As a result, Greece did not have any territorial or other commitments, other than the common cause to fight the Ottoman Empire.

In April 1912 Montenegro and Bulgaria reached an agreement including financial aid to Montenegro in case of war with the Ottoman Empire. A gentlemen's agreement with Greece was reached soon after, as mentioned before. By the end of September a political and military alliance between Montenegro and Serbia was achieved.^[7] By the end of September 1912, Bulgaria had formal-written alliances with Serbia, Greece, and Montenegro. A formal alliance was also signed between Serbia and Montenegro, while Greco-Montenegrin and Greco-Serbian agreements were basically oral "gentlemen's agreements". All these completed the formation of the Balkan League.