The later part of his reign was characterized by the failure of military expedition against the Dafala tribes and the influence of Paramananda Sannyasi, a saintly figure from Brindaban, over Udayaditya Singha.
Udayaditya's over exerted devotion towards Paramananda Sanyasi, aroused dissatisfaction among the nobles, which ultimately caused his deposition and execution.
His reign was followed by a series of political anarchy and internal disturbances in the Ahom kingdom which continued till the accession of Gadadhar Singha in 1681 CE.
[3] He also fought against the invading forces of Koch kingdom led by Chilarai during the reign of his elder brother Suklenmung and his nephew Sukhaamphaa.
He also characterized the promises made by Ram Singh I as a highway made of ashes as they might not be accepted by the Mughal Emperor Aurangzeb, or by the next Mughal commander who will succeed Ram Singh I. Swargadeo Udayaditya Singha confirmed the views of the Premier Atan Burhagohain and directed the commanders to bring the war to a victorious conclusion.
[10] When the Ahom rejected the proposal of Ram Singh I, the latter in desperation commanded a contingent of his cavalry to cross the Brahmaputra in boats and enter the plains of Guwahati by breaking through the opening at the Andharubali rampart.
[14] Most of the prominent nobles like Atan Burhagohain remained in Guwahati in order to repel any possible Mughals invasion in Lower Assam In 1671 CE, a treasure house at Hilikha, containing a great store of gold and silver, was burnt down.
Enquiry showed that the Bharali Barua, the officer in charge of the store-house was responsible for the fire, which was caused by his carelessly leaving a lighted pipe near some inflammable material.
The Dafalas now complained that they were on the verge of starvation owing to the long delay in the delivery of the stipulated blackmail and the payment of the taxes due from the Bahatias.
[16] Swargadeo Udayaditya Singha immediately arranged an expedition under Ghorakonwar Borbarua to capture and punish the Dafala raiders.
The Prime Minister Atan Burhagohain tried to dissuade the monarch stating reasons that the Dafalas lived in inaccessible villages situated in the midst of dense forest and steep mountain defiles, and the hill-men could always evade the pursuers by flying from one shelter to another.
The agents of Dafala chief Bakara Gam met Tua and Tita and expressed regrets for having acted disloyally against the Ahom monarch.
How will it be possible on the part of elephants to proceed by paths meant for the passage of dogs and jackals?” Tua and Tita sent a secret message through Ramdhan Ganak Hatkhowa to Ghorakonwar Borbarua asking him to fall upon the Dafalas during the continuance of the negotiations.
The Borbarua sent a force who proceeded by boat, but the Dafalas had meanwhile left the venue on the pretext of coming back with the men and goods captured by them from the Assamese.
He instructed the chief of his personal body-guards, Papang Chaodang Barua, to arrest the Borbarua and kept him as a prisoner in the Hatisal or Elephant stalls.
After some time, Ghorakonwar was readmitted into the good graces of the king, and was made Bhitarual Phukan or the Commander of the household troops.
The king became greatly devoted to Paramananda, considered him as Guru or religious mentor and constructed for him a large monastery near the entrance of the Capital known as Chunpora-duar.
Forced by Royal orders, the three Dangarias or ministers, Atan Burhagohain, Baghchowal Borpatrogohain and Langichang Borgohain and Laithepena Solal Gohain and many Phukans, Rajkhowas and Baruas became disciples of Paramananada Sannyasi.
The king reiterated his conviction of the omniscience of his Guru Paramananda and the consequent propriety on the part of the Mahantas to become the Sannyasi's disciples.
Being himself a disciple of Makajan Mahanta of the Thakuria denomination, he knelt down before the Mahantas and solicited their blessings for the success of his enterprise, saying,- “Your Holinesses should only bestow upon me the dust of your feet, and I shall do whatever redress is necessary.”[29] The king got scent of the mischief that was brewing against him and his protégé; and with the object of keeping Debera away from the capital for some time he ordered him to command an expedition against the Mishmi rebels living near Sadiya.
Debera was witty enough to understand the real intention of the monarch, and informed the king that he would start on the expedition after three days as he was convalescent at that time having just recovered from polypus of the nose.
[30] On that very night, Debera met the three Dangarias and persuaded them to support Sarugohain, the younger brother of Swargadeo Udayaditya Singha, in his attempt to seize the throne.
The prince gave vent to his resentment on the conduct of Udayaditya Singha,-“The Bairagi has become to my brother, not a mere hermit, but an object of extreme veneration, the Saheb of his head.
Swargadeo Udayaditya Singha, soundly asleep in his bed, heard faintly the uproar and commotion outside, but the body-guard on duty in the Royal bed-chamber, who had already been tutored by Debera, informed the monarch that the disturbance was due to the elephants coming out of their stalls, and the attempt made by the Borbarua to bring them round.
Having besieged Udayaditya Singha in his bed chamber and making it impossible for him to escape, Sarugohain seated in the audience hall, declared himself to be king.
[42][43] Swargadeo Udayaditya Singha's reign was remarkable chiefly for the expulsion of invading Mughal forces from Kamrup and the victory of Ahoms in the Battle of Saraighat.
[45] Contemporary historians remarked that he lacked the strength and intelligence of his elder brother Swargadeo Chakradhwaj Singha,[46] yet one must not forget that he extended full supports and aids to the Ahom generals in Guwahati who were fighting against the Mughal invaders.
While it reflected his fighting spirit and determination, but subsequent events also showed that he was stubborn and lacked the knowledge of political diplomacy and military skills.
His stubbornness to bring the old Vaishnava Mahantas or Monks of Assam under the influence of Paramananda Sannyasi was a political blunder of highest magnitude which ultimately cost him his throne and his life.
The period of ministerial supremacy will continue till 1681 CE, when Gadadhar Singha from Tungkhungia line of Ahom Dynasty ascended the throne and put an end to the domination of ministers over the monarch.