He succeeded his father as Ban of Croatia in the aftermath of his death on 1 May 1312 and inherited a strongly-founded dominion encompassing all of Croatia, Bosnia, Zahumlje and the Dalmatian cities.
His wife Helen, was a relative of the Anjou royal house, and Mladen already made marriage contracts of their children to the counts of Gorizia, which could serve as valuable allies in the war against the Republic of Venice.

Mladen greatly weakened the Venetian attempts to take Zadar, by buying off the leader of their mercenaries, which greatly reduced their potential on land.
However, in September 1313, he allowed the return of Zadar to Venice, under the condition of granting the city considerable autonomy.
He relinquished the title Duke of Zadar, but was granted citizenship of Zadar under Venetian patronage by 1314.
In doing this, he kept a strong and stable relations with the city and made status quo with Venice.

His rule was met with mutiny for the first time in spring of 1315 when the Captain and Potestat of the city of Trogir, Matthew of Zori, expelled members of the Andreis family in an internal struggle within the city.
Although this was not an act directed against Mladen's rule, the expelled received his support and as a result, he answered with hostility.
Mladen requested from the commune "to send him a blank piece of paper, on which he will write whatever he wants from the city" and forty hostages, which was rejected by the city council.
Fearing Mladen's wrath, they also decided to destroy the monastery outside the city walls, to prevent it from being used as a military base against the city.
Despite the incident, it did not escalate, and Mladen allowed Matej to keep his position.
However, he imposed a large fine on the city.
Matej Zori made contacts with the members of Mladen's court in order to secure better status.
In 1317, Matej Zori was eventually ousted from his position and was driven into exile by certain outer elements, with the help of the city of Šibenik, an act which was supported by Mladen.
He imposed further sanctions of the city and Matej's supporters in 1318.

Apart from Trogir, he also faced problems with the Croatian nobility.
He inherited a dispute from his father regarding Jablanac, with the noble Frederick III (Frankopan) of Krk, although this did not pose any significant threat.
A larger threat emerged from a rebellion of counts Nelipić and Kurjaković in the winter of 1316-1317, probably in connection with his conflicts against the Slavonian Babonić nobles.
Howerer, it was concluded shortly thereafter, and the mutineers did not seem to have fallen in his disfavor.

Following the death of Stephen Dragutin, he occupied the northern territories of today's Bosnia and Hercegovina, Usora and Soli.
This act prompted a retaliation of the neighboring Raška, which attacked Šubić's territories from Ston.
In 1318, he joined the crusade of Phillip of Taranto, titular Latin Emperor and cousin of his wife, against the King of Rascia, Milutin.
Mladen invaded Raška from his territories in Zahumlje and was initially successful, but had to withdraw in the subsequent years.
In the aftermath, his younger brother George II (who was the prince of Omiš) was given as a hostage to the opposing side as part of the peace negotiations, and was subsequently transferred to the city of Dubrovnik for safe keeping.

Mladen's rule was unpopular with Bosnia's nobility, specifically among the supporters of the former Bosnian ban Stephen Kotromanić.
As a result, he placed Kotromanić under his patronage and arranged a marriage between him and one of the daughters of Meinhard of Ortenburg.
He also took a tolerant stance towards Bosnia's krstjani (members of the Bosnian Church), which brought him into conflict with the Pope.
Later, in order to restore and quiet situation in Bosnia, he appointed Stephen in 1322 as the Bosnian Ban.
He succeeded his father as Ban of Croatia in the aftermath of his death on 1 May 1312 and inherited a strongly-founded dominion encompassing all of Croatia, Bosnia, Zahumlje and the Dalmatian cities. His wife Helen, was a relative of the Anjou royal house, and Mladen already made marriage contracts of their children to the counts of Gorizia, which could serve as valuable allies in the war against the Republic of Venice.
Mladen greatly weakened the Venetian attempts to take Zadar, by buying off the leader of their mercenaries, which greatly reduced their potential on land. However, in September 1313, he allowed the return of Zadar to Venice, under the condition of granting the city considerable autonomy. He relinquished the title Duke of Zadar, but was granted citizenship of Zadar under Venetian patronage by 1314. In doing this, he kept a strong and stable relations with the city and made status quo with Venice.
His rule was met with mutiny for the first time in spring of 1315 when the Captain and Potestat of the city of Trogir, Matthew of Zori, expelled members of the Andreis family in an internal struggle within the city. Although this was not an act directed against Mladen's rule, the expelled received his support and as a result, he answered with hostility. Mladen requested from the commune "to send him a blank piece of paper, on which he will write whatever he wants from the city" and forty hostages, which was rejected by the city council. Fearing Mladen's wrath, they also decided to destroy the monastery outside the city walls, to prevent it from being used as a military base against the city. Despite the incident, it did not escalate, and Mladen allowed Matej to keep his position. However, he imposed a large fine on the city. Matej Zori made contacts with the members of Mladen's court in order to secure better status. In 1317, Matej Zori was eventually ousted from his position and was driven into exile by certain outer elements, with the help of the city of Šibenik, an act which was supported by Mladen. He imposed further sanctions of the city and Matej's supporters in 1318.
Apart from Trogir, he also faced problems with the Croatian nobility. He inherited a dispute from his father regarding Jablanac, with the noble Frederick III (Frankopan) of Krk, although this did not pose any significant threat. A larger threat emerged from a rebellion of counts Nelipić and Kurjaković in the winter of 1316-1317, probably in connection with his conflicts against the Slavonian Babonić nobles. Howerer, it was concluded shortly thereafter, and the mutineers did not seem to have fallen in his disfavor.
Following the death of Stephen Dragutin, he occupied the northern territories of today's Bosnia and Hercegovina, Usora and Soli. This act prompted a retaliation of the neighboring Raška, which attacked Šubić's territories from Ston. In 1318, he joined the crusade of Phillip of Taranto, titular Latin Emperor and cousin of his wife, against the King of Rascia, Milutin. Mladen invaded Raška from his territories in Zahumlje and was initially successful, but had to withdraw in the subsequent years. In the aftermath, his younger brother George II (who was the prince of Omiš) was given as a hostage to the opposing side as part of the peace negotiations, and was subsequently transferred to the city of Dubrovnik for safe keeping.
Mladen's rule was unpopular with Bosnia's nobility, specifically among the supporters of the former Bosnian ban Stephen Kotromanić. As a result, he placed Kotromanić under his patronage and arranged a marriage between him and one of the daughters of Meinhard of Ortenburg. He also took a tolerant stance towards Bosnia's krstjani (members of the Bosnian Church), which brought him into conflict with the Pope. Later, in order to restore and quiet situation in Bosnia, he appointed Stephen in 1322 as the Bosnian Ban.
Mladen II Šubić of Bribir