In the 1940s Nsimbi produced Ennono z’Abaganda (The Origins of Baganda), a foundational work in the development of Luganda orthography and historiography. He established the Luganda Society in 1950 to preserve, popularise and promote the use of Luganda among both Baganda and non-Baganda, and worked with J. D. Chesswas to produce text books for courses in Luganda language. Chairman of the society from 1963 - 1987, Nsimbi was a driving force, together with Dr. Livingstone Walusimbi, in establishing a Luganda language curriculum for the first time at Makeerere University in 1976, the country’s only university at the time. As a result a high school curriculum was introduced in 1979, and a curriculum for the National Teachers' Colleges in 1984. In 1989 he was awarded an honorary doctoral degree (Doctor of Letters, Honours Causy) from Makeerere.
Nsimbi also encouraged the revivial of other local languages and cultures in the nation of Uganda. He was made an MBE in 1960, and was awarded the Independence Medal in 1963. He died on March 5, 1994, and the same year was honoured with the creation of the Dr. Nsimbi Scholarship Scheme in honor of his work in promoting Luganda language and culture.