A pretender to the throne, Boris Kalamanos, who had already claimed Hungary during Béla the Blind's reign, temporarily captured Pressburg (now Bratislava in Slovakia) with the assistance of German mercenaries in early 1146.

Louis VII refused to extradite Boris to Géza, but prevented the pretender from contacting his supporters in Hungary and managed to shepherd him to Constantinople with the rest of the crusaders.

Géza joined the coalition that Louis VII and Roger II of Sicily formed against Conrad III of Germany and Byzantine emperor Manuel I Komnenos.

Géza intervened at least six times in battles for control of Kiev on behalf of Iziaslav II either by sending reinforcements or by personally leading his troops to the Kievan Rus' between 1148 and 1155.

Conflicts eventually emerged between Géza and his brothers, Stephen and Ladislaus, who both took flight from Hungary and settled in Emperor Manuel's court in Constantinople.

Géza was born the eldest son of Béla the Blind, a cousin of King Stephen II of Hungary, and Helena of Serbia in 1130.

[5] In the same year, Queen Helena took Géza and his younger brother, Ladislaus, to an assembly held at Arad, where she ordered the massacre of sixty-eight noblemen "by whose counsel the King had been blinded",[6] according to the Illuminated Chronicle.

[8] According to the chronicler Bishop Otto of Freising, Boris approached Conrad III of Germany to seek his assistance against Géza at the end of 1145.

[10] Upon the recommendation of Vladislav II of Bohemia, the German monarch authorized Boris to muster an army of mercenaries in Bavaria and Austria.

[14][10] The royal forces soon imposed a blockade on the fortress and convinced Boris's mercenaries to surrender without resistance in exchange for compensation.

[16] Before crossing the river Lajta (now Leitha in Austria), which marked the western border of Hungary, the sixteen-year-old Géza was girded with a sword in token of his coming of age.

[17] In the Battle of the Fischa on 11 September, the Hungarian army under the command of Géza and Beloš routed the German troops led by Henry Jasomirgott, Margrave of Austria.

[18] German–Hungarian relations remained tense[8] as Boris attempted to take advantage of Conrad III's decision to lead a crusade to the Holy Land through Hungary.

[19] However Géza, who knew that "he could conquer more easily by gold than by force, poured out much money among the Germans and thus escaped an attack from them,"[20] according to the chronicler Odo of Deuil.

[21][22] The Illuminated Chronicle relates that some Hungarian noblemen promised Boris "if he could make his way into the kingdom, many would take him for their lord and, deserting the King, would cleave to him.

[34] The Hypatian Codex says that Géza referred to his war against Emperor Manuel when excusing himself for refusing to send reinforcements to Iziaslav II whom Yuri Dolgorukiy, Prince of Suzdal, expelled from Kiev in August 1149.

[31] A "countless allied force of Hungarian cavalry as well as of the heterodox Chalisoi"[36] had supported the Serbs in the same year, according to the contemporaneous John Kinnamos, but the Byzantine army routed their united troops on the river Tara in September.

[51] Abū Hāmid even urged the soldiers to make "every effort to go on jihad" with Géza "for thus God [would] set down the merit of Holy War to [their] account".

[55] According to the Diploma Andreanum of 1224, which spelled out the privileges of the Transylvanian Saxons, their ancestors were invited by Géza to settle in southern Transylvania.

[59] Although Andronius Komnenus's plot was discovered and he was captured, Géza invaded the Byzantine Empire and laid siege to Braničevo in late 1154.

[59] In the same year, a Byzantine army expelled Géza's ally, Desa, from Serbia and restored Uroš II, who had promised that he would not enter into an alliance with Hungary.

[66][67] According to the nearly contemporaneous Rahewin, Géza's youngest brother, Stephen, began conspiring with their uncle, Beloš, and other lords of the realm.

[66] To avoid a civil war, Géza first ordered the persecution of Stephen's supporters, then had his rebellious brother expelled from the kingdom and later sentenced him to death.

[69][68] Géza's uncle, Beloš, was not mentioned in royal charters issued after March 1157, which suggest that he had left Hungary after that date.

[50][73] Before long, Géza's brother, Stephen, left for the Byzantine Empire and settled in Constantinople where he married Emperor Manuel's niece Maria Komnene.

[83][84] Géza only decided to change sides after most European monarchs, including the kings of Sicily, England and France, joined Alexander III.

[88] Shortly before his death, Géza granted Dalmatia, Croatia and other territories to his younger son, Béla, as an appanage duchy.