John Edward Fitt, son of James R.R. Fitt and his wife Elizabeth, trained as a civil engineer by means of an apprenticeship and became an associate member of the (British) Institution of Civil Engineers. Following his arrival in South Africa he was an assistant engineer in the Public Works Department of the Cape Colony from January 1897 to 1903, after which he became a partner of Robert Cochrane in the firm Cochrane & Fitt of Cape Town. The firm was declared insolvent in 1905.
Fitt joined the South African Association for the Advancement of Science in 1902 as a foundation member. At the association's first annual meeting in Cape Town the next year he delivered a paper on "Sewage disposal in Cape Colony", which was published in the association's Report for 1903 (pp. 369-372). The paper dealt with the methods of sewage purification recently introduced in Europe and elsewhere, using septic tanks, contact beds with nitrifying bacterial cultures, and filtration. Fitt also joined the Cape Society of Civil Engineers in 1903, the year it was founded, and remained a member when it changed its name to the South African Society of Civil Engineers in 1909.
During 1906-1907 Fitt was town engineer of Standerton, in the Transvaal Colony. Later in his career, during 1926-1928, he planned a power station, electric light scheme and additional water supply for Stutterheim in the Eastern Cape. He was survived by his wife Annie Jane, born Hodson (whom he had married in Buenos Aires), and two daughters.