The 28-year old started his career in his home country with Real de Banjul, before moving to Belgium with Anderlecht in 1999.
Six appearances and one goal came for the Belgium giants before a move to Roda in Holland where his career really kicked off, as he became a firm fan favourite in the process of making 112 appearances and scoring 20 goals over seven years with the club.
In 2007, he spent time at Xanthi before moving to England with Walsall where he spent one season, scoring five times in 37 goals, including one deflected goal against Tranmere at the Bescott stadium in April.
During January of the 07/08 season, Sonko won the League One player of the month award, although consistency was not part of his game according to many fans.
The Saddlers released Sonko at the end of the 2007/08 season from where he joins Tranmere on a one-year deal. He can play on either wing and has scored seven goals in fourteen international appearances for his country.
Sonko is an exciting addition to the Tranmere squad, and he certainly put in an impressive appearance against Ronnie Moore's side for Walsall at the Bescott Stadium in April.
The midfielder is Tranmere's second signing of the summer after Gareth Edds joined from MK Dons a few weeks ago.