Eric Moreillon was the brother of Bertrand Moreillon, a Swiss missionary in the Paris Evangelical Mission to Basutoland (now Lesotho). Eric visited Lesotho three times for health reasons, in 1905, 1910, and 1923-1924. During these visits he collected some plants at Cana, a mission station a few kilometers north-east of Teyateyaneng, in the north-west of Lesotho. A hundred of his specimens went to the University of Zuerich and more than half of these are grasses.
Moreillon contributed a note, "Connaissances astronomiques des Bassoutos" (astronomical knowledge of the Basuto) to the journal L'Astronomie in 1914. His address at this time is given as Kenega Drift (near Matatiele), East Griqualand.