Born on Dec. 28th 1863 in Copenhagen, Denmark.
He initially took drawing lessons from his father (the painter Frederik Vermehren). He studied at the technical school and was finally admitted to the Royal Danish Academy of Fine Arts in Copenhagen in Sep. 1881 and ended his studies there in May 1891.
In recognition of his talent and work he won several prizes and scholarships: the Neuhausen Prize in 1889 and the Academy Scholarships in 1891, 1896, 1899 and 1903. In 1894 he won the Raben-Levetzau Prize and in 1908 the Serdin Hansen Prize.
He debuted at the esteemed Charlottenborg Spring Exhibitions (Copenhagen) in 1888 and exhibited there almost henceforth. Apart from exhibiting at other prominent national exhibitions he also exhibited at the Glaspalast in Munich in 1913.
Gustav Vermehren probably followed in his father, Frederick Vermehrens track, but he tried not to renew folk painting from the period between the two Schleswig wars, but contented himself with the watered-down, civil, anecdotal, sentimental genre paintings of Carl Bloch's spirit. The nostalgic traits are prevalent when he paints houses in the countryside, peasant living rooms and kitchens. Hornsherred, Amager and the area around Hvalsø were among his favorite areas. The contrast with specially L.A. Ring is here marked. When Einar Nielsen and the Funen peasant painters emerged, the contrast was more striking and Vermehren had to defend his conservatism with fierce counterattack. The technical skills he had acquired from his father, was still reason enough for his and Sophus Vermehrens preparatory school from 1892 to gain much interest.