Notker of Saint Gall, who bewailed the decline of the dynasty a generation later, called Carloman bellicosissimus (literally "most warlike", or in historian Eric Goldberg's words a "real ass-kicker").

[6] In October 848, Carloman was present at his father's council in Regensburg, where the Slavic commander (dux) Pribina was rewarded for his service in defending the Bavarian frontier.

This name was chosen because it was distinctly dynastic (the founder of the Carolingian family was Bishop Arnulf of Metz), yet had never been used by a reigning king and was thus appropriate for an illegitimate eldest son.

[9] Around 860, Arnulf and his cousin, Hugh, the illegitimate son of Carloman's brother Louis, were both in Koblenz at the court of their grandfather, who was probably overseeing their military education and also holding them to ensure the good behaviour of their fathers.

[10][4] Since this was his first governorship, Louis did not give him rule over the entire March of Pannonia, with traditional seat of frontier governor (prefect) at Tulln.

[6] Gaining the first foothold of power in Carantania, Carloman moved to assume a more prominent role in governorship over the frontier regions of his father's realm.

[12] That move was made without his fathers consent, and by 862 an open conflict erupted, with Carloman siding with Rastislav of Moravia and taking control over all southeastern regions, advancing further into Bavaria, up to the river Inn.

[14] Replaced by count Gundachar, who was appointed governor of eastern marches by king Louis (863), prince Carloman remained in his father custody until 864, when he escaped and returned to Carantania.

In 871, he managed to capture Svatopluk, thus establishing direct control over the entire principality, but soon decided to reinstall him, in order to pacify the country.

[17] In 873, after several interventions of Pope John VIII, including those made to Carloman, a peace settlement was reached in Forchheim, between king Louis and envoys of Svatopluk, thus concluding the state of war on eastern borders.

Carloman married the daughter of a Bavarian military leader (dux) named Ernest, whom the Annales Bertiniani describe as "the greatest of all the king's great men".

[23] Carloman led an army into Italy, where he granted a diploma to the monastery of San Clemente a Casauria, one of Louis II's most favored houses.

On 6 October 877, Charles the Bald died and later that month Carloman succeeded in having himself elected King of Italy by the nobles assembled in Pavia.

The lure of Italy was "the looting which was apparently acceptable when a king first took over a kingdom", providing rewards that could be shared out among followers and more than offset the cost of raising an army and crossing the Alps.

[24][25] Carloman was one of only two Carolingian kings of Italy—his brother and successor Charles being the other—who did not issue a capitulary at the beginning of his reign in order to proclaim his legitimacy and affirm his keeping to traditions of good government.

[26] In Italy, Carloman confirmed his predecessor's act that made bishops permanent missi dominici (royal representatives) in their dioceses.

After his succession, Carloman supported the dukes, Lambert I and Guy III, who had always claimed the rights as royal representatives which Charles had offered the pope.

[30] In a letter of 7 June 879, Pope John, having failed to convince Louis the Stammerer, Charles the Bald's heir, to come to Italy for its defence, appealed to Carloman, whom he had previously rejected.

This policy had supporters, like Abbot Regino of Prüm and the monks of Saint Gall, but also detractors, who appealed to Carloman's brother Louis.

Carloman tried to legitimise Arnulf's actions by adding his son's name to the prayer provisions of his charters, but in November Louis came to Bavaria to force a resolution of the succession.

[38] Regino's entire encomium on Carloman goes: That most excellent king was learned in letters, devoted to the Christian religion, just, peaceful, and morally upright.