The retired prolific striker will take up his first senior coaching role after previously learning his trade at the Gunners. The Frenchman coached Arsenal's Under 18 team before he was forced to leave his role due to Arsene Wenger's demands for Henry to leave his role as a pundit on Sky Sports.
Henry will be allowed to continue his work with Sky and join up with the Belgium national team during this season's international breaks. The 39-year-old will team up with former Everton boss Martinez and the Spaniard's trusted assistant Graeme Jones.
Friday's surprise announcement was made as Martinez named his first senior squad since taking the Belgium job after Euro 2016. Henry will coach the likes of Eden Hazard, Marouane Fellaini and Kevin De Bruyne after Martinez named his first squad for matches against Spain and Cyprus.
Martinez said of Henry's appointment: "Thierry has been in the situation to change the spirit into winning something. I'm very satisfied that (the Belgian federation) has been able to create an impressive staff."
It was also announced that fitness coach Richard Evans, who like Jones followed Martinez from Swansea to Everton via Wigan, would take up a similar role with the national team.
Henry, Arsenal's all-time leading scorer with 228 goals in all competitions, wrote on Twitter: "Honoured to be assistant coach @BelRedDevils. Thanks to Roberto Martinez & the Royal Belgian Football Association. Very excited. Can't wait."
Martinez's first game in charge of Belgium will be a friendly against Spain on September 1 and the opening World Cup qualifier against Cyprus on September 6.
- Dailymail