The youngster has agreed personal terms with the Royals and will tomorrow complete his transfer to Reading if he passes a medical. He will put pen to paper on a two-year deal and will likely line-up in the Royals defence alongside Adie Williams or Ivar Ingimarsson next season.
Other clubs, including Championship rivals Preston North End, were reportedly interested in signing Sonko, but Steve Coppell beat off all competitors to make the Senagelese man, who has African Cup of Nations experience, his second summer signing.
Sonko will link-up with his former Bees manager Wally Downes who was this week appointed as a coach at Reading.
Current Brentford manager Martin Allen was no doubt disappointed to lose Sonko to the Royals but believes the move down the M4 is a good one for the youngster.
Praising his departing centre-back he said: "Whilst working with him the last two months of the season he has shown an incredible work ethic, never missed a day's training, and was always willing to stay out on the training pitch and do extra work. These are the players that progress."
"I hope that he continues his development at Reading Football Club into what I potentially think could be a top-quality Premiership player," concluded Allen, speaking to Brentford's official site.
Ibrahima spent two years with Bees, having signed for them from French side Grenoble in August 2002. He made ninety-one appearances for the Griffin Park side and scored nine goals, an impressive tally for a centre-back.
At 6ft 4 inches tall the centre-back will be an imposing figure in Reading's back line next season.
Sonko joins the ever-growing former Brentford contingent at the Madejski Stadium that now consists of seven men. Coach Wally Downes and manager Steve Coppell have both managed the Bees whilst Nicky Forster, Steve Sidwell, Lloyd Owusu, Ivar Ingimarsson and now Ibrahima Sonko have all played for Brentford.