Sonko joined the Gambia Police Force in 1982 and was promoted to the rank of Corporal in 1984, and to Cadet Officer in 1988.

He was appointed as the force's first Public Relations Officer (PRO) in 1993 and was posted to Kanifing Division as second-in-command in 1994.

[1] In 1998, Sonko became the officer commanding the Fraud Squad, and the next year he was appointed as Crime Management Coordinator (CMC) at the rank of Assistant Superintendent of Police (ASP).

He was posted as the acting Commissioner of the PIU, and then became officer commanding in the Prosecution Division.

[1] On 18 December 2009, Sonko was promoted to Deputy Inspector General of Police.