In 1250 or 1251, during the course of internal power struggles, he was baptised as a Roman Catholic; this action enabled him to establish an alliance with the Livonian Order, a long-standing antagonist of the Lithuanians.

He broke peace with the Livonian Order in 1261, possibly renouncing Christianity, and was assassinated in 1263 by his nephew Treniota and another rival, Duke Daumantas of Pskov.

Now generally considered the founder of the Lithuanian state, he is also now credited with stopping the advance of the Tatars towards the Baltic Sea, establishing international recognition of Lithuania, and turning it towards Western civilization.

[10] Kronika polska, litewska, żmódzka i wszystkiej Rusi, published by Maciej Stryjkowski in 1582, asserts that in 1240 Mindaugas, also known as Mindow, Mendolph, Mendog, and Mindak, ascended to his father's throne in Navahrudak Rus', Grand Duchy of Lithuania, and Samogitia.

The Bychowiec Chronicles, dating from the 16th and 17th centuries, have been discredited in this regard, since they assert an ancestry from the Palemonids, a noble family said to have originated within the Roman Empire.

[18][need quotation to verify] Since Old Church Slavonic sources provide the most information about Mindaugas's life, they were judged the most reliable by linguists reconstructing his original Lithuanian name.

[18][need quotation to verify] In 1909 the Lithuanian linguist Kazimieras Būga published a research paper supporting the suffix -as, which has since been widely accepted.

[21] They were loosely bonded by commonalities of religion and tradition, trade, kinship, joint military campaigns, and the presence of captured prisoners from neighboring areas.

Their efforts in Lithuania were temporarily halted by defeat at the Battle of Saule in 1236, but armed Christian orders continued to pose a threat.

[8][25] Historian S.C. Rowell has described his rise to power as taking place through "the familiar processes of marriage, murder and military conquest.

[16] Warfare in the region intensified; he battled German forces in Kurland, while the Mongols destroyed Kiev in 1240 and entered Poland in 1241, defeating two Polish armies and burning Kraków.

[22] The Lithuanian victory in the Battle of Saule temporarily stabilized the northern front, but the Christian orders continued to make gains along the Baltic coast, founding the city of Klaipėda (Memel).

Mindaugas established his residence in Navahrudak and succeededed in becoming master of the so-called Black Ruthenia on the upper Neman and its affluents with the cities of Hrodna, Vawkavysk, and Slonim, and also of the Principality of Polotsk.

His attempts to consolidate his rule in Lithuania met with mixed success; in 1249, an internal war erupted when he sought to seize his nephews' and Vykintas' lands.

[29] Attacked from the north and south and facing the possibility of unrest elsewhere, Mindaugas was placed in an extremely difficult position, but managed to use the conflicts between the Livonian Order and the Archbishop of Riga to further his own interests.

He succeeded in bribing Order Master Andreas von Stierland, who was still angry at Vykintas for the defeat at the Battle of Saule in 1236, by sending him "many gifts".

[27][29][33] In 1250 or 1251, Mindaugas agreed to receive baptism and relinquish control over some lands in western Lithuania, in return for an acknowledgment by Pope Innocent IV as king.

Internal conflicts persisted; during the spring or summer of 1251, Tautvilas and his remaining allies attacked Mindaugas's warriors and the Livonian Order's crossbow-men in Voruta Castle.

The deeds might have been falsified by the order;[28] the case for this scenario is bolstered by the fact that some of the documents mention lands that were not actually under the control of Mindaugas[25] and by various irregularities in treaty witnesses and seals.

[28] A direct confrontation with the Mongols occurred in 1258 or 1259, when Berke Khan sent his general Burundai to challenge Lithuanian rule, ordering Daniel and other regional princes to participate.

[44] The ongoing formal archeological digs at Kernavė began in 1979 after a portion of the site named "Mindaugas Throne hill-fort" collapsed.

Local merchants could only conduct transactions via Order-approved intermediaries; inheritance laws were changed; and the choices among marriage partners and residencies were restricted.

[48][49] The case for his apostasy rests largely on two near-contemporary sources: a 1324 assertion by Pope John XXII that Mindaugas had returned to error, and the Galician–Volhynian Chronicle.

[5][49] The cathedral he had built in Vilnius was superseded by a pagan temple, and all the diplomatic achievements made after his coronation were lost, although the practice of Christianity and intermarriage were well tolerated.

[15] Treniota emerged as the leader of the Samogitian resistance; he led an army to Cēsis (now in Latvia), reaching the Estonian coast, and battled Masovia (now in Poland).

[27] The Rhymed Chronicle mentions Mindaugas's displeasure at the fact that Treniota did not create any alliances in Latvia or Estonia; he may have come to prefer diplomacy.

[7] His known family relations end with his children; no historic records note any connections between his descendants and the Gediminids dynasty that ruled Lithuania and Poland until 1572.

[55] A 17th-century rector of Vilnius University held him responsible for the troubles then being experienced by the Polish–Lithuanian Commonwealth ("the seed of internal discord among the Lithuanians had been sown".

[7] The first academic study of his life by a Lithuanian scholar, Jonas Totoraitis (Die Litauer unter dem König Mindowe bis zum Jahre 1263) was not published until 1905.

The 750th anniversary of his coronation was marked in 2003 by the dedication of the Mindaugas Bridge in Vilnius, numerous festivals and concerts, and visits from other heads of state.