Following in Van Vollenhoven's footsteps, Holleman developed an interest in adat law, the indigenous legal system used in the Dutch East Indies and beyond.

[3] Holleman remained in Leiden until he was appointed as an extraordinary professor in indigenous (Bantu) law and native administration at Stellenbosch University in South Africa in 1939.

Towards the end of his life, Holleman began to work on a project to codify the indigenous law of South Africa.

In 1957, he was appointed honorary fellow at the University of Natal 'in recognition of his contribution to the science and teaching of the law systems of underdeveloped societies.'

His son Johan Frederik Holleman[5][6] continued his father's work in adat and Southern African indigenous law.