Between 1978 and 1980 he continued to rise in the ranks, serving as a platoon commander and then as a mechanical and transport officer (MTO) in the second battalion, Republic of Sierra Leone Regiment (2RSLAR).

After distinguishing himself in this service by arresting the organizers of an $11.5 million diamond racket in Kono despite being offered a bribe of $100,000 and a brand new Mercedes-Benz, Nelson-Williams moved up to the position of adjutant of the 1RSLAR in 1984, preparing him for further roles in military administration.

After this recall, he rejoined the ECOMOG force in several positions, distinguishing himself in particular at the Bo waterside by being the first officer to capture the Mano River Union Bridge, a major objective.

[5] He was invited to the University of Ibadan in Nigeria to read for a Master of Science degree in strategic and defence studies which he completed with a thesis on "the role of the military in sustaining peace and democracy in post-war Sierra Leone."

Upon his return to Sierra Leone in 2002, he was appointed assistant Chief of Defense Staff (ACDS) Ops & Plans and promoted to the substantive rank of Brigadier General.

In 2005, he relinquished his appointment of ACDS Ops & Plans and fully concentrated on his new responsibility as the Deputy Chief of Defence Staff and military spokesman.

He was presented with the honour of "Grand Officer of the Order of Rokel" in 2007, and appointed to the position of Chief of the Defence Staff on Friday, 12 September 2008, by President Ernest Bai Koroma, succeeding Major General Edward Sam M'boma.

He is a co-author of the book "Security Sector Review in Sierra Leone −1996-2007" sponsored by the British Government, Foreign Ministry and the Department for International Development.