The Blues first tried to bring the 34-year-old to Portman Road back in January and resumed their interest this summer after his contract expired at West Ham.
The former Newcastle and Bournemouth front man, who has scored 95 Premier League goals in his career, had also been eyed by newly-promoted duo Coventry and Hull too.
Wilson, however, has opted to pen a one-year deal with the Bees following their recent ninth place finish.
Brentford head coach Keith Andrews said: “Callum is someone that everyone will be familiar with; he has been a Premier League goalscorer for such a long time.
“He gives us more options in that area of the pitch, and will help Igor Thiago and Kaye Furo with the experience that he has.
“He’s just got that nous to score goals, as well as that experience around the training ground.
“This is another really good signing for us.”