He sits on the Permanent Court of International Arbitration in The Hague and is recognized as Sudan's most prominent Christian lawyer.

Abel Alier was instrumental in the creation of the 1972 Addis Ababa Agreement which permitted southern Sudan to have its own autonomous government based out of Juba.

In 2005 he headed the committee that was appointed to investigate the death of John Garang who had died in a helicopter crash after leaving Uganda for Sudan.

Alier and his team did their part to investigate the possible mechanical failure that led to the crash which had been blamed on bad weather and lack of visibility although the Ugandan President Yoweri Museveni hinted that the possibility of foul play was something that shouldn't be dismissed or disregarded.

In the early 1990s, Abel Alier wrote a book under the title Southern Sudan: Too Many Agreements Dishonored.