He identified a number of poems by Gerbrand Bredero, which had been assumed to reflect incidents in the poet's own life, as translations of French originals, fundamentally changing the understanding of Bredero's character and literary career.
In 1942 he graduated Licentiate in Germanic Philology, with an additional certificate for teaching in secondary education.
[2] In 1952 he completed a doctoral dissertation on Willem van Nieulandt II, and in 1961 he became a lecturer at the Facultés Universitaires Saint-Louis in Brussels.
[2] Keersmaekers was a member of numerous literary and scholarly societies, and in 1978 he was elected to the Royal Academy of Dutch Language and Literature, in succession to the recently deceased Stephanus Axters.
[3] Over the course of his lifetime Keersmaekers wrote at least 498 publications, not counting over 200 book reviews.