Mathabar Singh Thapa listenⓘ (Nepali: माथवरसिंह थापा, 1798–1845)[a] was the Prime Minister of Nepal and the Commander-In-Chief of the Nepalese Army from 25 December 1843 – 17 May 1845, until he was murdered by his nephew Jung Bahadur Rana.

[4][note 2] He was the nephew of Bhimsen Thapa, who was sentenced to prison after falsely being accused of killing King Rajendra's six months old son.

[11][8] On 27 November 1835, Mathabar Singh left Kathmandu with a retinue of two thousand men, including 200 officers and 600 soldiers, for London via Calcutta.

[15] Mathabar's extravagant expenditure was also heavily criticized by Queen Samrajya Lakshmi Devi, since at that time the state coffer was in dire condition; and to pacify her, Bhimsen had to reimburse the extra expenses from his own pockets.

[17][18] It was at once rumored that the child had died of poison intended for his mother the Senior Queen Samrajya Laxmi Devi: given at the instigation of Bhimsen Thapa, or someone of his party.

[18][19][20] On this charge, Mathbar Singh with his family, the court physicians, Ekdev and Eksurya Upadhyay, and his deputy Bhajuman Baidya, with a few more of the nearest relatives of the Thapas were incarcerated, proclaimed outcasts, and their properties confiscated.

[18][19][21][22] Fearful that the Pandes would re-establish their power, Fatte Jang Shah, Ranganath Poudel, and the Junior Queen Rajya Laxmi Devi obtained from the King the liberation of Bhimsen, Mathabar, and the rest of the party, about eight months after they were incarcerated for the poisoning case.

Upon his release, the soldiers loyal to Bhimsen crowded behind him in jubilation and followed him up to his house; a similar treatment was given to Mathabar Singh and Sherjung Thapa.

[30] Mathabar Singh's nephew Kaji Jung Bahadur Kunwar was sent to persuade his uncle after which he arrived in Kathmandu Valley in April 1843.

[31] Mathawar Singh living in a public rest house, constantly urged that he would not enter his residence in Kathmandu until the framed charges against his family be released.

[30] In July 1843, the case was re-discussed at the Bharadari Sabha (Council) in front of King Rajendra and Queen Rajya Laxmi, where Thapa family were declared innocent and their confiscated properties were restored.

We hereby appoint you as Mukhtiyar of all civil and administrative affairs throughout our country, as well as Prime Minister, Commander-In-Chief and General with Jagir emoluments amounting to Rs 12,401.

Remain in attendance during the war and other occasions as commanded by us, be faithful to our salt and utilize the following lands and revenues as your Jagir with due loyalty.

(Particulars of lands and revenue follow).Aswin Badi 7, 1901(September 1844) Before he was made the Minister and the Commander-In-Chief, he had led to the murder of almost all of his enemies and political adversaries.

"[34] Ultimately, the extreme power of Gagan Singh led to him being assassinated by King Rajendra and Prime Minister Fatte Jungh Shah in 1846 September 14 at 10 P.M..

He had following sons as per various sources: The land grants received by Mathbar Singh Thapa on various dates were:[38] Guthi for the Sri Ambar Narayan temple