[1] He was appointed assistant on the Gold Coast in 1857, serving as commandant of Fort Patience at Apam from 1858 onwards.

During the European leave of governor Cornelis Nagtglas, Magnin temporarily became second in command of the colony, serving as bookkeeper, secretary and public prosecutor under governor ad interim Cornelis Meeuwsen.

Magnin served from 4 May 1865 until 19 February 1866, when the newly appointed governor Willem Hendrik Johan van Idsinga arrived on the Gold Coast.

Magnin was then honourably discharged, retiring from service on the Gold Coast and returning to Europe.

[2][3][1] In the Netherlands, Magnin was appointed mayor of Hoogwoud in 1866, of Beverwijk and Wijk aan Zee en Duin in 1867 and of Veendam in 1880.