Callcott M. Stevens received his secondary education at the South African College, Cape Town, from 1866 to 1868. On 1 August of the latter year he joined the British civil service and was stationed at the Royal Observatory, Cape of Good Hope. In 1873 he was appointed third assistant at the observatory and was engaged in astronomical work until he requested to be transferred to the Cape civil service in February 1876. He remained a civil servant for the rest of his career, but retained an interest in scientific subjects for some years.
Stevens was an early member of the South African Philosophical Society, established in Cape Town in September 1877. On 28 November that year he read his first paper before the society, entitled "Remarks on 'clicks', with an investigation of the etymon of some South African native geographical names". The paper was published in the first volume of the society's Transactions (pp. 51-60). At the next meeting, on 30 January 1878, he read two further papers, though these were not published. One was "On the meteorology of the sea-side", the other "On the determination of distance by observations of the velocity of sound". The latter paper was no doubt inspired by accurate determinations of the velocity of sound made in 1871 by the director of the Cape Observatory, E.J. Stone*. In July 1878 Stevens was appointed secretary of the society's Ethnological Section. In response to a circular he sent out to elicit ethnographic information only one significant response was received, from Mr James Lycett* of Worcester who sent in tracings and photographs of rock paintings. Stevens was still a member of the society in 1883, but no longer in 1887.
In 1882 he joined Allbert Marth* of the British Transit of Venus Expedition to observe the transit on 6 December that year. Marth set up his instruments near the railway line at what was then known as Montagu Road. The settlement was renamed Touws River in 1883. The two concrete piers on which the instruments were mounted were declared a national monument in 1938, after H.E. Wood had drawn attention to their historical significance the previous year.
During his long career in the Cape civil service Stevens held, among others, the following positions: clerk in the treasury (June 1876); in command of the civil service detachment of the Duke of Edinburgh's Own Volunteer Rifles during the Basuto campaign of 1880-1881; accountant to the receiver-general of revenue (February 1882); stamping commissioner (July 1889); chief clerk in the civil commissioner's office (March 1894); member (and acting chairman) of the Rinderpest Committee (1897); an official in the attorney-general's office, stationed in Clanwilliam (1899), from where he applied (unsuccessfully it seems) for a similar position in the administration of the Orange Free State and Natal Colony; in the attorney-general's office in Cape Town (1902); in command of the Prince of Wales Own Regiment of the Cape Peninsula Rifles, rising to the rank of lieutenant-colonel in 1905; assistant supervisor of the census of 1904; resident magistrate of Montagu (August 1904); and resident magistrate, customs officer, shipping master, and deputy inspector of mines at Knysna (July 1907). He appears to have retired soon after the formation of the Union of South Africa in 1910, but in 1914 was appointed a member of the Liquor Licensing Court for the district of Knysna. In 1905 and 1906 he and Arthur H.B. Stevens, presumably a relative, traded as Rochester Brick Company.