[2] Thesleff was born in Helsinki, the eldest daughter of five siblings[3] and her father was an amateur painter.

She took private lessons and then, in 1887, studied for two years at the Finnish Art Society Drawing School (now known as the Finnish Academy of Fine Arts) with Gunnar Berndtson.

In 1891, Thesleff moved to Paris and enrolled into Académie Colarossi.

[2] Thesleff took part in many big exhibitions in the 20th century; in particular, in 1949 her paintings were on display in a large exhibition of Nordic art in Copenhagen and were praised by the media.

[1] At the beginning of her career, Thesleff worked on symbolist paintings in the style similar to Eugène Carrière, though she insisted she was most influenced by Édouard Manet.