Tolmer was the son of French refugees in England and spent his early years in England and France. He joined the British legion formed to assist in the conflict for the throne of Portugal during the 1830s. Tolmer achieved the rank of corporal and was awarded the Order of the Tower and Sword. He migrated to South Australia in 1840. Shortly after his arrival Tolmer was appointed sub-inspector of police and before long promoted to inspector of the mounted police. In the same year he was made adjutant of the cavalry of the volunteer militia.

During his time with the mounted police, Tolmer pursued cattle-rustlers, smugglers and other criminals. He was involved in the capture of two Aboriginal men who were thought to have killed the survivors of the wreck of the ship Maria. His work also took him to the colonies of Victoria and Tasmania. Tolmer was appointed Commissioner of Police in January 1852 after acting in the position previously. His acts as Commissioner included the employment of 'native' police and the establishment of the water police and detective branch. Tolmer is perhaps best remembered, however, for the gold escorts he led during the first years of the gold rush in Victoria. After gold was discovered in 1852 many South Australian men went east seeking their fortunes on the Victorian goldfields. This left Adelaide, in particular, with a shortage of working men, but also with a shortage of money. The men were making discoveries of gold in Victoria, but they had no way of getting it to their families in Adelaide. Tolmer suggested that a contingent of South Australian police, led by him, could escort gold from Victoria to Adelaide where it could be sold and thus circulated through the South Australian economy. The price offered for gold in Adelaide was higher than at the goldfields or in Melbourne, so the South Australian diggers were encouraged to send their finds back. The first gold escort left Adelaide on 10 February 1852 and arrived in the goldfields 10 days later. The escorts continued until December 1853; in total 18 were made.

Tolmer's long absences from Adelaide with the gold escort, his quick temper and the disorganization of the police force led to his removal as Commissioner in November 1853. He remained with the police force as inspector and then superintendent until 1856. Tolmer bought property in the colony's south-east, but his grazing venture had little success. In 1859 he was back in the police force for nine months and also led an unsuccessful attempt to traverse Australia from south to north. Tolmer was employed as crown lands ranger in 1862 and held a number of other government positions associated with lands until his retirement in 1885.

3 January 1852: Appointed Commissioner of Police

10 February 1852: Led the first gold escort to bring gold found by South Australian miners in Victoria back to SA

1862: Appointed crown lands ranger

'Death of Captain Tolmer', Adelaide Observer, 15 March 1890, p. 7, col. b-e

Some adventures of Alexander Tolmer in colonial South Australia 1840-1856 : selected from his "Reminiscences of an adventurous and chequered career at home and at the antipodes" / edited, with additional text, by Murray Tonkin, [Adelaide: M.P. Tonkin], 1985

Tolmer, Alexander. Reminiscences of an adventurous and chequered career at home and at the antipodes, Adelaide, [S. Aust.]: Libraries Board of South Australia, 1972

Australian Dictionary of Biography Online: Search for Tolmer, Alexander