When Mes'ud was informed about the death of Sultan Tugrul, he immediately set off and went to Hamedan and ascended the throne of the Iraq Seljuks State (1134). His first affair was the suppression of the rebellion of his nephew, Davud. To this effect, he married his daughter with Davud and appointed him as the crown prince.
On the other hand, the Abbasi Caliph Mustersid had collaborated with some Turkish emirs with the purpose of the achievement of political authority again. He got prepared for a war against the Seljuk sultan. Meanwhile, Davud had made some preparations in order to collaborate with the Caliph in Azerbaijan. The Caliph set in motion against Mes'ud without awaiting Davud. The war between the two sides took place in Day-Merg around Hamedan (1135). However, this appeared to be a minor short-term fight rather than a war. The Turkish soldiers within the army of the Caliph had taken side with the Sultan Mes'ud. Upon this change, the Caliph lost the war and he was taken as a prisoner. Sultan Mes'ud showed great respect to the caliph and he took him to his attendance and advanced against his nephew, Davud. In the course of this movement, the caliph was killed by Batini supporters in a military encampment near Meraga.
The new caliph, Resid assumed a hostile attitude against Sultan Mes'ud. Then, the Prince Davud, Imad ed-Din Zengi and some major emirs came to Baghdad and established an alliance against Sultan Mes'ud. As a result of this alliance, the prayers were delivered in the name of Davud in Baghdad. Upon this movement, Sultan Mes'ud required to besiege Baghdad and the caliph had to go to Mosul together with Zengi. Sultan Mes'ud penetrated into Baghdad. Redis was dismissed from the caliphate and Muktefi Billah was assigned to the post of caliphate (1136). On the other hand, an army under the command of Kara Sungur who was one of the commanders of Mes'ud was able to defeat Davud in Meraga.
The Ruler Seljuk-shah desired to capture Iraq, too. However, his situation in Huzistan was not so strong and Davud tried to establish domination in this region. His brother Seljuk-shah asked help from Sultan Mes'ud (1135). In the following year, Seljuk-shah appeared in the regions of Vasit and Hille. This expedition failed against the regent of Sultan Mes'ud in Iraq. Under these circumstances, Seljuk-shah went to the side of Sultan Mes'ud. Mes'ud behaved him kind and gave him the regions of Ahlat, Manzikert and Erzen (1107-8). The former caliph Resid who looked for supporters and opportunities in order to fight against Mes'ud was killed in Isfahan in the same year.
One of the persons who did not recognise the sultanate of Mes'ud was Mengubars who was the ruler of Fars. He rebelled in the end of 1137. The two sides fought in the place called as Gurshenbih. The Tutor Mengubars was defeated in this war and taken as prisoner. He was immediately killed by Sultan Mes'ud.
The greatest assistant of Mengubars, Emir-aba gathered the forces that had been dispersed and defeated the army of Mes'ud that was occupied in despoiling the properties of Mengubars through a sudden attack. Sultan Mes'ud could run away with difficulty together with Kara Sungur and he retreated to Azerbaijan. Boz-aba took some of the emirs of Sultan Mes'ud as prisoner and then, killed them (April-May 1138). Then, he returned to Fars with a great speed and dominated in this country.
Towards the middle of his sultanate years, Sultan Mes'ud had fairly been under the domination of Turkish emirs. The Tutor Kara Sungur that was one of these emirs and the ruler of Erran and Azerbaijan died in Erdebil in the year of 1140-1. Upon his testament, Sultan Mes'ud appointed Cavli Candar to replace him. Mes'ud started to get prepared against Zengi that he considered as the main source of the continuous rebellions within the state (1143). Zengi preferred to make an agreement with sultan and he accepted to pay a significant fee with the amount of 100 thousands of dinars. On the other hand, the Prince Davud was killed by Batini supporters in Tabriz (1143). After a while, we have observed that a sincere relationship was established between the Fars ruler, Boz-aba and the Rey governor, Abbas. As a result, Boz-aba and Abbas set in motion in order to dethrone Mes'ud. They apparently declared that they had come to present their submission to Sultan Mes'ud. Sultan Mes'ud had understood their main purpose of arrival, but he did not have enough force to resist them. The last war between Sultan Mes'ud and Boz-aba took place in the pastures of Kara-tegin with a distance of one day's journey from Hamedan. As a result of this war, Boz-aba was taken as prisoner and killed (1147). After eradication of nearly all troubles within the state, Sultan Mes'ûd did not live for long and he got sick and died in Hamedan (1152).