Sindhuli District (Nepali: सिन्धुली जिल्लाListen^ⓘ) is a district of Bagmati Province in Nepal. The district, with Sindhulimadhi (Kamalamai) as its headquarters, covers an area of 2,491 km² (962 sq mi). It is divided into nine local bodies with two municipalities and seven rural municipalities. As per the 2021 census, Sindhuli district has a population of 300,026.

Sindhuli district is composed of Inner Terai and hilly areas. It is classified as Inner Terai District for administrative purposes. It borders 10 other districts, making it the district that borders the most districts. It borders Koshi Province to the east and Madhesh Province to the south.

The district is famous for the historic Sindhuli Gadhi Fort where troops of British East India Company were defeated by Gorkhali Army in 1767 A.D (1824 B.S). The iconic BP Highway passes through this district. Sindhuli is also known for the production of Junar (sweet orange).

According to the former administrative divisions of Nepal, Sindhuli fell under Janakpur Zone in Central Development Region. Sindhuli Gadhi was the headquarter of the district till 1967 A.D (2023 B.S).

Sindhuli District is named after the Sindhuli Valley (Sindhulimadhi and surrounding areas). Various accounts are associated with the naming of Sindhuli and there is no definite evidence explaining how the place got its name “Sindhuli (सिन्धुली)”.

Sindhuli has been the historical and important route linking the Kathmandu Valley with the eastern hills and the southern plains, giving it strategic and economic significance. Local forts and hill strongholds, including Sindhuli Gadhi, were controlled by regional powers and functioned as defensive outposts and transit points for trade and movement. Doyas of Karnat Dynasty in 1244 A.D and Shamsuddin Ilyas Shah, Sultan of Bengal in 1349 A.D, used the route of Sindhuli Gadhi to attack Kathmandu Valley. Prior to unification of Nepal, Sindhuli was the part of Makawanpur Kingdom, ruled by kings of the Sen dynasty.

The Battle of Sindhuli, fought in 1767 A.D (1824 B.S), stands as one of the most important military victories in the history of Nepal. It was a confrontation between the Gorkhali forces, led under the broader unification campaign of King Prithvi Narayan Shah, and the troops of the British East India Company. The battle demonstrated the strength, strategy, and determination of the Gorkhali army and played a crucial role in protecting Nepal’s independence.

During the mid-18th century, King Prithvi Narayan Shah was actively working to unify the many small kingdoms of the Himalayan region into a single nation. At the same time, the British East India Company was expanding its influence in the Indian subcontinent. When the King of Kantipur (Kathmandu), Jaya Prakash Malla sought British help to counter the Gorkhali advance, a British force under Captain Kinloch was sent toward Kathmandu. To reach the valley, the troops had to pass through the difficult hill region of Sindhuli Gadhi.