Ekström was born in the small village Segerstad in the south easts part of the island Öland in Sweden. His father was a house painter. He took drawing lessons as a child, then studied at the Royal Swedish Academy of Fine Arts from 1865 to 1872, but was influenced by French painting rather than the prevailing Düsseldorf School. In 1876, thanks to the support of King Oscar II, he was able to go to Paris, where he lived until 1890. There, he came under the influence of the Barbizon School and Camille Corot. His first exhibit at the Salon was in 1878 and he won a gold medal at the Exposition Universelle (1889).