Keulemans worked in England from 1869. He regularly provided illustrations for The Ibis and The Proceedings of the Zoological Society. He illustrated many important bird books, including Buller's A History of the Birds of New Zealand (1873). He also spent some time collecting birds in West Africa.
Keulemans writes a work that comprises three volumes and is called Onze Vogels in Huis en Tuin (1869-1876), which he provides with 200 hand coloured lithos.
Keulemans, who sometimes paints for days in his atelier just dressed in pants, speaks various languages, likes music, gazes at stars and is involved in spiritualism.