Watson, who operates as a right-back and a right wing-back, is without a club after departing MK Dons earlier this summer.
The 26-year-old has been looking for a new side and several teams have been credited with holding an interest in signing him.
It is Charlton though who are winning the race and they are poised to take Watson to the Valley.
He will add to the club’s full-back options and it is unclear what length of contract he will sign with the Addicks.
Watson made 30 appearances in League One for MK Dons over the course of last season, but was unable to help them avoid relegation.
He is an experienced League One campaigner, with 85 outings in the division to his name.
Watson came through the youth ranks at Reading, who he will meet this season in League One following their relegation.
