Don Stephen Senanayake PC (Sinhala: දොන් ස්ටීවන් සේනානායක; Tamil: டி. எஸ். சேனநாயக்கா; 20 October 1884 – 22 March 1952) was a Ceylonese statesman. He was the first Prime Minister of Ceylon, having emerged as the leader of the Sri Lankan independence movement that led to the establishment of self-rule in Ceylon. He is considered as the "Father of the Nation".

Born to an entrepreneur from the village of Botale, Senanayake was educated at S. Thomas' College, Mutwal before briefly working as a clerk in the Surveyor General's Department. Joining the family business, he managed the family estates and the Kahatagaha Graphite Mine. Along with his brothers, Senanayake became active in the temperance movement which grew into the independence movement following 1915 Sinhalese-Muslim riots, in which the Senanayake brothers were imprisoned without charges for 46 days. He was elected unopposed in 1924 to the Legislative Council of Ceylon from Negombo, becoming the Secretary of the unofficial members group of the Legislative Council. In 1931, he was elected to the State Council of Ceylon, where he served as Minister of Agriculture and Lands. He was elected to the first Parliament of Ceylon forming a government and serving as Ceylon's first Prime Minister from 1947 until his death in 1952.

He was born in the village of Botale in the Hapitigam Korale (currently known as Mirigama) on 20 October 1884 to Don Spater Senanayake (1847–1907) and Dona Catherina Elizabeth Perera Gunasekera Senanayake (1852–1949). Spater Senanayake had made his fortune in graphite mining and at the time he was expanding into plantations and investments in the arrack renting franchise. Later he would be awarded the title of Mudaliyar for his philanthropy. Stephen Senanayake had two elder brothers, Don Charles "D. C." Senanayake and Fredrick Richard "F. R." Senanayake; and one sister, Maria Frances Senanayake who married F. H. Dias Bandaranaike.

Brought up in a devout Buddhist family, he entered the prestigious Anglican school S. Thomas' College, Mutwal. Never a studious student, he excelled in sports playing cricket and played in the Royal-Thomian. He later played cricket for the Sinhalese Sports Club and Nondescripts Cricket Club. His contemporaries at S. Thomas's includes D. R. Wijewardena, Sir Paul Pieris, Sir Arthur Wijewardena and Sir Francis Molamure.

After completing schooling, he worked as a clerk in the Surveyor General's Department but left after a period of apprenticing. He joined his brother D. C. Senanayake in running his father's extensive business holdings. He worked as a planter, introducing the new commercial crop of rubber to the family plantations. He managed the Kahatagaha Graphite Mine, which was owned by his brother F. R. Senanayake wife's family. F. R. Senanayake had married the youngest daughter of Mudaliyar Don Charles Gemoris Attygalle. He was a member of the Low-Country Products Association and of the Orient Club. In 1914, he was appointed as a member of a government commission sent to Madagascar to study and report on their graphite mining industry.

The three Senanayake brothers were involved in the temperance movement formed in 1912. When World War I broke out in 1914 they joined the Colombo Town Guard. The brothers were arrested and imprisoned without charges during the 1915 riots. They faced the prospect of execution, since the British Governor Sir Robert Chalmers considered the temperance movement as seditious. He was released on a bail bound after 46 days at the Welikada Prison without charges. The heavy-handed suppression of the riots by the British colonial authorities initiated the modern independence movement led by the educated middle class. Don Stephen and Don Charles were prominent members of the political party Lanka Mahajana Sabha. Fredrick Richard and Don Charles were committed supporters of the Young Men's Buddhist Association. D. S. Senanayake played an active role in the independence movement, initially in support of his brother Fredrick Richard.

In 1924, Senanayake was elected unopposed to the Legislative Council of Ceylon from Negombo. He became the Secretary (similar to a whip) of the unofficial members group of the Legislative Council, activity engaged in proceedings with a particular interest in subjects related to agriculture, lands, and irrigation. He questioned in the Legislative Council the biased policies of the colonial administration in the plantain industry, the cost overruns of the Batticaloa line and the Trincomalee line, the delays in the Norton Bridge Dam, and advocated for the establishment of the first university in the island close to Kandy. In 1927, he acted on behalf of Gerard Wijeyekoon in the Executive Council. When his brother F.R. died on a pilgrimage to Buddha Gaya in 1925, Don Stephen assumed his leadership of the independence movement.

In 1931 he was elected to the newly formed State Council of Ceylon representing the Ceylon National Congress. At the first siting of the State Council, he was elected as Minister of Agriculture and Lands to chair the state council committee on Agriculture and Lands.