Ross was born in Almora, India. He was the eldest son of General Sir Campbell Claye Grant Ross of the Indian Army and Matilda Charlotte Elderton (d. 1906), daughter of Edward Merrick Elderton, a London solicitor. His grandfather was Lieutenant Colonel Hugh Ross. At the age of eight, Ross was sent to England for his education. After completing his early education in two small schools at Ryde, he was sent to a boarding school at Springhill, near Southampton in 1869.

Ross commenced his study of medicine at St. Bartholomew's Hospital in London on 29 October 1875. He passed his final examination in 1880 and qualified as MRCS and LSA. He joined the Indian Medical Service in 1881. His first posting was in Madras.

Ross studied malaria between 1881 and 1899. He worked on malaria in Calcutta at the Presidency General Hospital where he was ably assisted by Kishori Mohan Bandyopadhyay, a Bengali Indian scientist. Ross built a bungalow with a laboratory at Mahanad village (about 4 km from Pandua Railway Station on the Bandel-Burdwan line). He used to stay in the village from time to time, collecting mosquitoes in Mahanad and adjoining villages and conducting research. In 1883, Ross was posted as the Acting Garrison Surgeon at Bangalore during which time he noticed the possibility of controlling mosquitoes by controlling their access to water.

In 1897, Ross was posted in Ooty and fell ill with malaria. After this he was transferred to Secunderabad, where Osmania University and its medical school is located. He discovered the presence of the malarial parasite within a specific species of mosquito, the Anopheles. He initially called them dapple-wings and following the hypothesis of Sir Patrick Manson that the agent that causes malaria was spread by the mosquito, he was able to find the malaria parasite in a mosquito that he artificially fed on a malaria patient named Hussain Khan. Later using birds that were sick with malaria, he was soon able to ascertain the entire life cycle of the malarial parasite, including its presence in the mosquito's salivary glands. He demonstrated that malaria is transmitted from infected birds to healthy ones by the bite of a mosquito, a finding that suggested the disease's mode of transmission to humans. Subsequently Sir Ronald Ross Institute of Tropical Medicine was established as a division of the faculty of medicine at Osmanaia Medical College, Hyderabad.

In 1902, Ross was awarded the Nobel Prize in Medicine for his remarkable work on malaria. His Indian assistant Kishori Mohan Bandyopadhyay was awarded a gold medal by the King of the United Kingdom.

In 1899, Ross went back to Britain and joined Liverpool School of Tropical Medicine as a professor of tropical medicine. In 1901 Ross was elected a Fellow of the Royal College of Surgeons and also a Fellow of the Royal Society, of which he became Vice President from 1911 to 1913. In 1902 he was appointed a Companion of the Most Honourable Order of Bath by King Edward VII, and discovered how malaria was transmitted. In 1911 he was elevated to the rank of Knight Commander of the same Order.

During his active career Ross advocated the task of prevention of malaria in different countries. He carried out surveys and initiated schemes in many places, including West Africa, the Suez Canal zone, Greece, Mauritius, Cyprus, and in the areas affected by the First World War. He also initiated organizations, which have proved to be well established, for the prevention of malaria within the planting industries of India and Ceylon. He made many contributions to the epidemiology of malaria and to methods of its survey and assessment, but perhaps his greatest was the development of mathematical models for the study of its epidemiology, initiated in his report on Mauritius in 1908, elaborated in his Prevention of malaria in 1911 and further elaborated in a more generalized form in scientific papers published by the Royal Society in 1915 and 1916. These papers represented a profound mathematical interest which was not confined to epidemiology, but led him to make material contributions to both pure and applied mathematics.

Through these works Ross continued his great contribution in the form of the discovery of the transmission of malaria by the mosquito, but he also found time and mental energy for many other pursuits, being a poet, playwright, writer and painter. Particularly, his poetic works gained him wide acclamation which was independent of his medical and mathematical standing.

Ross married Rosa Bessie Bloxam in 1889. They had two sons, Ronald and Charles, and two daughters, Dorothy and Sylvia. His wife died in 1931. Ross survived until a year later, when he died, after a long illness, at the Ross Institute, London, in 1932.

Ross received many honours in addition to the Nobel Prize, and was given Honorary Membership of learned societies of most countries of Europe, and of many other continents. He got an honorary M.D. degree in Stockholm in 1910 at the centenary celebration of the Caroline Institute and his 1923 autobiography Memoirs, Etc. was awarded that year's James Tait Black Memorial Prize. Whilst his vivacity and single-minded search for truth caused friction with some people, he enjoyed a vast circle of friends in Europe, Asia and the United States who respected him for his personality as well as for his genius.

In India Ross is remembered with great respect. Because of his relentless work on malaria, the deadly epidemic which used to claim thousands of lives every year could be successfully controlled. There are roads named after him in many Indian towns and cities. In Calcutta the road linking Presidency General Hospital with Kidderpore Road has been renamed after him as Sir Ronald Ross Sarani. Earlier this road was known as Hospital Road. In his memory, the regional infectious disease hospital at Hyderabad was named after him as Sir Ronald Ross Institute of Tropical and Communicable Diseases in recognition of his services in the field of tropical diseases. The building where he worked and actually discovered the malarial parasite, located in Secunderabad near the old Begumpet airport, is a heritage site and the road leading up to the building is named Sir Ronald Ross Road.

In Ludhiana, Christian Medical College has named its Hostel as "Ross Hostel". The young doctors often call themselves "Rossians". The University of Surrey, UK, has named a road after him in its Manor Park Residences.