Immediately after his accession to the throne, Mahipala set out to initiate Bengal's recovery from being completely shattered. The Bangarh and Tippera Inscriptions provide facts regarding the military conquests. It is known from these inscriptions that Mahipala I had recovered northern, western, and parts of eastern Bengal. He overpowered the hilly tribes called Kambojas and Chandras, who had usurped the Pala territories after Devapala's rule. Mahipala I was able to recover only the Northern and Eastern parts of Bengal. The Bahgaura inscription of Coomilla testifies his hold over the region. After conquering North Bengal he used it as his entrance to East Bengal. The Belba Grant testifies his hold over the region of Varendri or north Bengal. The Tirumalai Inscription of Rajendra Chola indirectly points to the hold of Mahipala over western Bengal. This inscription states that Dandabhukti or Danton in south Midnapore and the other adjacent regions were ruled by independent kings whom he had defeated. Therefore it is generally believed that Mahipala had restored a part of Bengal, except a portion of southern west Bengal, where Ranasura and Dharmapala ruled
Epigraphic evidences prove that Mahipala I ruled over the whole of Bihar. South Bihar was however inherited by Mahipala I from his father Vigrahapala II and had probably also conquered north Bihar. The Sarnath inscription depicts that Mahipala I had given orders for the construction of sacred structures in Bihar.
The significant event of Mahipala's reign was the invasion of Rajendra Chola in Bengal. The Chola army led by general of Rajendra Chola lingered for two years, from 1021 to 1023 A.D. The Cholas had defeated some local kings of Bengal. They included Dharmapala of Dandabhukti, Rana Sura of Southern Radha and Govindachandra of Vangla. Those local kingdoms were not included within the kingdom of Mahipala I in Bengal. The Chola records refer that they had conquered the areas of Tandabhutti, Takkanaladha, Uttiraladha and Vanga Desa. Then the Cholas waged war against the Pala king Mahipala in Bengal and conquered the region of Northern Radha. Mahipala I was defeated and other vanquished kings of Bengal were compelled to accept supremacy of the Cholas. Though the hold of Mahipala over Bengal was curtailed, yet northern Bengal and northern Radha still owed allegiance towards Mahipala I.
Towards the end of his rule Mahipala had to face a foreign invasion led by Gangeyadeva Kalachuri. Mahipala had to suffer several reverses in his hands. From the statement of Arabian traveller Baihaqi, it is made clear that Banaras, which formerly belonged to the Palas, was ruled by Gangeyadeva Kalachauri in 1034 A.D.
He was a gallant leader of the Pala revival. His name is associated with many tanks and towns in Bengal. He was a great patron of Buddhism which reflects in repair of religious houses like Nalanda, Sarnath, and Benares and other monasteries also. His reign is discernible for the revival of Buddhism in Bengal. Many scholars like Tilopa and Jnana Sri Mishra visited Bengal during Mahipala's rule.
Mahipala had saved the Pala kingdom from being shattered completely, but also had revived the former glory, magnificence and power of the Dynasty to a substantial extent. However Mahipala has been accused of indifference towards national cause. He cared regional and local interests. This is so because, Mahipala did not join the Hindu confederacy, organised by the Shahi kings of Punjab in order to resist the Muslim invasion of Sultan Mahmud. Some historians have pointed out that it was his Buddhist inclination, which had prevented him from being part of the Hindu confederacy against the Muslims. However Mahipala I has been credited to have arrested forces of disintegration within the Pala Empire and to have revived the imperial dream of the Palas, by extending the boundary of his kingdom on all sides.